In Canada’s fight with Trump, Danielle Smith is playing the good cop.

Three more parties, all projected to secure small numbers of seats in the country’s parliament, the House of Commons, are in the fray: the left-wing New Democratic Party; the Greens; and the Bloc Quebecois, which is focused on gaining sovereignty for Quebec.

Just three months ago, the Conservatives had been leading polls by more than 25 percentage points, and Mr. Poilievre appeared all but certain to become Canada’s next prime minister. Justin Trudeau and the Liberals had led the country for a decade, becoming increasingly unpopular.

But Mr. Trudeau’s resignation in March and Mr. Trump’s tariffs and sovereignty threats against Canada upended the race. With Mr. Carney as the party leader and prime minister, the Liberals rapidly gained support as the ones to better handle Mr. Trump.

In Canada’s parliamentary system, voters choose who they want to represent their electoral district, known in Canada as a riding; the candidate who has the most votes wins, and the party that has the most seats becomes the ruling government, even if they do not control the majority. There are 343 seats in parliament.

But the two leaders vying to become Canada’s next prime minister are central to the choice Canadians are making on Monday, and they offer different personalities, experiences and visions for the nation at a critical juncture.

Here’s what else to know:

• The incumbent: Mr. Carney, 60, replaced Mr. Trudeau as prime minister just last month. He is a former central banker and executive with a global career. A dedicated centrist who has spent a lifetime in rarefied high-power circles, he has built his pitch as an anti-Trump, vowing to devote his financial expertise to improving his country’s economy and shielding it from Mr. Trump’s tariffs and annexation threats.

• The challenger: Mr. Poilievre, 45, is a career politician who supports deregulation and a smaller federal government. His tonal and ideological similarities to Mr. Trump — he denounces “woke ideology,” wants to defund the national broadcaster and slash foreign aid — have put off some voters, who see him as too similar to Mr. Trump at a time when the U.S. president is seen as an enemy of Canada.

• Closing times: Polls opened in a staggered manner to make vote counting easier across the vast country’s six time zones. Most will close at 9:30 p.m. Eastern time.

• Results: Ballots are counted by hand, not machines. Results should be known late Monday night. The New York Times will provide live results coverage with detailed information about every district race.

• Choosing leaders: Party leaders were chosen by party members in earlier votes. In federal elections, voters do not vote for Canada’s leader, as they might in a presidential system.

An unapologetic MAGA-aligned conservative, she has riled Canadians across the country by speaking admiringly of President Trump and focusing on her province’s fortunes, particularly its oil exports, even as the U.S. administration menaces Canada.

Ms. Smith, 54, has been premier for the past two and a half years, having spent the past two decades dipping in and out of politics.

“I keep getting fired,” she chuckled in an interview with The New York Times in Calgary, Alberta, in February.

She has also worked as an economist, a lobbyist and a radio host of a popular call-in show in which she honed her folksy, affable, but sharply ideological raconteur style.

She’s the closest thing Canada’s conservative movement has to a MAGA ally — and has the Mar-a-Lago photograph with Mr. Trump to prove it.

As Mr. Trump started to say he wanted to make Canada the 51st state, before his inauguration, Ms. Smith visited him in Florida.

Even before Mr. Trump’s re-election, Ms. Smith had been key in shaping the evolution of Canada’s broader conservative movement. Critics say she has courted ideological minorities, including fervent anti-vaccine organizations, advocates for Albertan secessionism and hard-line anti-trans activists, to secure her election.

She has been careful to make those groups feel included in her agenda while not fully endorsing their rhetoric.

That ability, along with the political freedom afforded by her lack of interest in national office, has put her at the vanguard of Canada’s changing right.

In recent months, Ms. Smith has defended her pro-Trump overtures as a diplomatic approach that complements the more aggressive stance taken by the federal government.

Simply put, she said of her Trump ties, “I’m happy to be good cop.”

The country’s westernmost province, British Columbia, will close a half-hour later than Ontario and Quebec do, at 10 p.m. Eastern.

(Elections Canada, the nonpartisan agency that administers the federal election, has a complete list of polling hours.)

About 7.3 million Canadians cast their ballots during the early-voting period, April 18 to April 21, according to Elections Canada, a 25 percent increase over early-voting turnout in the 2021 election.

Many Bloc supporters came to the conclusion that the French language and Quebec’s culture would have a better chance of surviving inside Canada, not as part of a 51st American state. Bloc strongholds around the island of Montreal suddenly became battlegrounds.

In one such electoral district south of Montreal, La Prairie-Atateken, where the Bloc won comfortably in the past two elections, polls showed a dead heat. A longtime Bloc supporter, Yannick Maheu, 52, voted for the Bloc, along with his daughter, Rosaly, 20, who was voting for the first time. But he said he had also been drawn by Mark Carney as the best equipped to deal with Mr. Trump and was pleased that polls show the Liberals heading toward a victory.

“I wouldn’t have supported the Liberals if Justin Trudeau were still prime minister,” he said. “But with Carney, under the current circumstances, I think a Liberal government will be good for us.”

Christine Lussier, 55, and her husband, Raymond Thibert, 67, voted for the Liberal candidate. They were worried about the economy and said their retirement savings had taken a hit because of Mr. Trump’s erratic economic policies. “Mr. Carney is a businessman, and he can help Canada more than Mr. Poilievre, who was too much like Trump,” Ms. Lussier said.

Mr. Carney’s opponents included his chief contender, Pierre Poilievre, the leader of the Conservative Party, which for much of the past year had dominated polls and appeared headed for a certain victory in the April 28 federal election. Mr. Carney’s move into politics and Mr. Trump’s economic and political assault on Canada have since reversed the fortunes of the Conservatives, with the Liberals enjoying a slight lead in the polls.

The other candidates were Jagmeet Singh of the New Democratic Party and Yves-François Blanchet, the leader of the Bloc Québécois, a party that promotes Quebec’s independence and runs candidates only in that province.

The key takeaways from the two-hour debate: No one had concrete ideas on pushing back against Trump. The candidates were divided on crime. They argued over the funding of public broadcasting. They debated building oil and gas pipelines. And the Trudeau legacy hung over the debate.

All of the politicians agreed that President Trump’s economic policies and his proposal to annex Canada have created a crisis.

But none of them offered any specific details about how they would get the American leader to change course, beyond general talk of tough negotiations at which they would assert Canada’s sovereignty and economic independence.

“They want to break us so that they can own us,” Mr. Carney said.

Mr. Carney leaned on his past as the governor of the Bank of Canada during the 2008 economic crisis and his time as the governor of the Bank of England during Brexit to present himself as the ideal negotiator.

Mr. Poilievre, a lifelong politician, criticized the Liberal government of the last decade as putting Canada “under the thumb” of the United States.

And he thought about the legendary Canadian hockey player Gordie Howe and his famous “elbows up” response to aggression on the ice.

And so Mr. Myers, the 61-year-old star of the “Wayne’s World,” “Austin Powers” and “Shrek” films and a beloved figure on both sides of the Canadian-American border, boldly opened his down vest and flashed his “Canada Is Not for Sale” T-shirt on live television. “Elbows up,” he mouthed into the camera, twice.

“What happened came from my ankles and from my brain and from my heart, and it was not about me — it was about my country,” he said. “I wanted to send a message home to say that I’m with you, you know.”

Winning over voters in Quebec has usually, in great part, meant winning hearts by speaking French, grasping the province’s history and appreciating its culture. That was never going to be easy for Mr. Carney, a political novice whose appeals to Québécois voters have been marked by his faltering French and a series of gaffes that have raised doubts about his basic knowledge of Quebec, the country’s second-most-populous province.

Until a few months ago, the Bloc Québécois — a party that runs candidates for the federal Parliament in Quebec but that supports independence for the province — appeared headed for a big victory that would have considerably hurt Mr. Carney’s chances of winning the April 28 federal election. But Mr. Carney and his Liberal Party now have a huge lead in the polls in Quebec.

The abrupt reversal is another sign of how Mr. Trump’s tariffs and aggressive threats of annexation have upended Canada’s elections. Most Canadians regard Mr. Carney, a former head of the Bank of Canada and the Bank of England who has never before run for office, as the most capable candidate to deal with the American president, polls show. Even many hardcore supporters of the Bloc Québécois are now considering Mr. Carney and are cutting him some slack for his lack of connection to Quebec.

“He seems competent,” said Yves Lefebvre, 67, a retired roofer who was shopping Monday at a supermarket in Sainte-Thérèse, a Bloc stronghold north of Montreal. “I don’t care if he speaks only English.”

Mr. Lefebvre, who said he usually votes for the Bloc, said he was hesitating this time because he was worried about Mr. Trump’s tariffs. That Mr. Carney appeared to know little about Quebec did not matter, Mr. Lefebvre said, adding, “I don’t understand English. I go to Ontario and I’m clueless.”

Analysts like to say that in Canada’s elections, Ontario, the province with the biggest population and 36 percent of the seats in Parliament, effectively decides who wins a federal election. It is difficult for any party that does poorly in Ontario to make up the difference in the rest of the country. But Quebec, with a 23 percent share of the seats, decides whether a party will get a majority, which would allow it to govern without a smaller party’s support.

“I really didn’t have any other options but to come to Chilliwack,” Ms. Robertson said.

Chilliwack, a farming community encircled by snow-capped peaks, was once looked down on by city dwellers because of its rural and isolated character. Now, it has become a magnet for people from Vancouver who can no longer afford living there.

Across Canada’s urban centers, climbing housing prices are pushing renters out and making buying a home a distant dream, especially for first-time buyers. The housing problem, which many in Canada describe as a full-blown crisis, is a top concern for voters heading to the polls to cast ballots in national elections.

Canada’s urban centers and, increasingly, its suburbs are now on lists of the most expensive places in the world to find a home.

In Toronto, the standard price for a single-family home, according to an index used by Canadian real estate agents to compare home sales, is around 1.4 million Canadian dollars, about $1 million, compared with 970,000 dollars, or $700,000, in 2020.

In Vancouver, the standard price is even higher, roughly two million dollars ($1.5 million) compared with 1.4 million ($1 million) five years ago.

The average rent in Vancouver is about 2,500 Canadian dollars per month, or $1,800, requiring a low six-figure salary to be considered affordable, according to Canada’s national housing agency.

While high living costs have become a source of concern in wealthy countries around the world, in Canada, many voters blame the ruling Liberal government for the country’s affordability crisis. Beyond soaring housing costs, Canadians also face higher prices for groceries and gas.

The economic misery could get worse because of tariffs imposed by President Trump on many Canadian exports that could lead to major job losses and even a recession.

Providing relief to beleaguered Canadians has been a main focus of the two men leading the two main parties competing in Monday’s election. Prime Minister Mark Carney of the Liberal Party and Pierre Poilievre of the Conservative Party have both promised tax breaks for first-time home buyers. The two parties have also pledged various other tax breaks for low-income and middle-class families.

“They’re throwing money at voters in this election campaign, which I see as a response to cost of living concerns,” said Kathryn Harrison, a political science professor at the University of British Columbia.

New Democrats who defect will likely support Mark Carney of the Liberal Party, who is in a neck-and-neck race against Pierre Poilievre, the leader of the Conservative Party.

Some Canadians fear the New Democratic Party’s waning influence could weaken the country’s core liberal pillars on issues from health care to immigration to climate change.

But the New Democrats have also drawn criticism from Conservative politicians and others who say that tax hikes to finance social programs will set back Canada’s struggling economy.

He also called Canada “a beautiful landmass” and referred to the border between the two countries as an “artificially drawn line from many years ago.”

Since taking office, Mr. Trump has repeatedly said Canada “doesn’t make sense” as a country but should just join the United States, threatening Canada’s sovereignty.

His tariffs against America’s closest ally and trading partner have pushed Canada closer to a recession, and his constant refrain about making Canada part of the United States have upended the political balance of power, boosting the previously moribund Liberal Party and hobbling the once dominant Conservatives.

He had made similar remarks questioning the permanence of the border between the two countries to former Prime Minister Justin Trudeau, putting Canada’s leadership on alert that the president of the United States was serious about taking over Canada.

Observers struggled to interpret Mr. Trump’s Monday missive.

Some felt it was veiled support for Pierre Poilievre, the Conservative Party leader, who is seen as a close ideological ally of Mr. Trump and has been criticized for being too Trump-like by many voters.

Others thought Mr. Trump’s post favored — perhaps inadvertently — Mark Carney, the current prime minister and Liberal leader, who’s shaped his campaign on an anti-Trump platform.

Whatever the case, one thing was clear: Mr. Trump is not giving up on his obsession with Canada, and the new government that emerges from Monday’s vote will need to deal with a leader intent on both hurting Canada’s economy with tariffs, and coveting its vast resources.

Mr. Trump’s post Monday was met with a swift rebuke by Mr. Poilievre.

“President Trump, stay out of our election,” the Conservative leader said on X.

“The only people who will decide the future of Canada are Canadians at the ballot box. Canada will always be proud, sovereign and independent and we will NEVER be the 51st state. Today Canadians can vote for change so we can strengthen our country, stand on our own two feet and stand up to America from a position of strength,” he added.

Mr. Carney also shared a post that reinforced Canadians’ independence and agency over who’s in charge in their homeland, but did not mention Mr. Trump, posting a video in which he said, “This is Canada, and we decide what happens here.”

He railed against an economy that he said was “a transfer of wealth from the have-nots to the have-yachts.” He whipped up thunderous applause with his vow to “cut foreign aid to dictators, terrorists and global bureaucracies, to bring our money home.”

He pledged that Canada’s beefed-up armed forces would be “guided by a warrior culture, not a woke culture.” His promise to eliminate the CBC, the public broadcaster he has accused of liberal bias, drew some of the most sustained applause.

“I love you, too,” Mr. Poilievre said after a long pause and a sip of water. “I love you, I love you, I love this province.”

Alberta, the oil-rich province in Western Canada, is the birthplace both of Mr. Poilievre, 45, and the right-wing populist movement that has come to dominate Canada’s Conservative Party.

Mr. Poilievre’s message of “common sense” against a purportedly corrupt elite resonates the most in Alberta, along with neighboring Saskatchewan, where support is also highest in Canada for the man who has upended its political landscape: President Trump.

But Mr. Poilievre’s deep ties to Alberta and its brand of conservatism are complicating his efforts to win voters in battleground provinces, especially Ontario and Quebec, ahead of the April 28 election.

In Ontario, the province with the largest number of voters, moderate conservatives allied with the provincial government have chosen not to help Mr. Poilievre’s campaign and are working with Mr. Carney’s government to challenge the tariffs by the Trump administration.

A high-ranking conservative official in Ontario said publicly that Mr. Poilievre was “too much like Trump.”

Now that most Canadians view Mr. Trump, who has vowed to annex Canada, as the greatest threat facing their country, being too much like the American president is considered a liability — except perhaps among some Conservatives.

“The difficulty for Mr. Poilievre in going beyond his base and becoming the strongest defender of Canada is his association with Trump,” Jean-Marc Léger, the president and chief executive of the firm, said in an interview.