Liberal Leader Mark Carney and Conservative Leader Pierre Poilievre had their first direct public exchange of the election campaign Wednesday, debating who would best represent Canada as prime minister amid historic trade tensions with the United States and strong concern over the cost of living.

Public-opinion polls show an increasingly polarized political landscape in which a two-party race has emerged between the Liberals and the Conservatives, leaving the NDP and Bloc Québécois trailing their typical levels of support and at risk of losing a significant number of seats in the next Parliament.

In that context, NDP Leader Jagmeet Singh and Bloc Québécois Leader Yves-François Blanchet both fought hard Wednesday to insert themselves into the conversation.

The two-hour French-language debate, which will be followed by an English debate Thursday, was seen as crucial for shoring up support in Quebec. With 78 seats in the House of Commons, the province is often seen as being able to make or break a party’s chances at a majority government.

Prior to Justin Trudeau’s January announcement that he would be stepping down as prime minister, Liberal fortunes in the province dropped so low that some predicted the Bloc could potentially form the Official Opposition.

Under Mr. Carney, however, Liberal support is increasing. Even criticisms of his French – it is perceived to be the weakest of the four leaders – have been sloughed off by many Quebec pundits.

Mr. Carney stood at the end of the row of men for the debate, a podium position that at times resulted in his competitors collectively staring him down as they launched their attacks – critiques that he only rarely responded to. In one toward the end of the debate, Mr. Poilievre argued that national unity was being threatened by a decade of Liberal governance and the party’s record on immigration, housing, inflation and crime.

“Aren’t you embarrassed to ask Canadians for a fourth mandate after having the worst record?” Mr. Poilievre asked.

“I just arrived,” Mr. Carney replied.

While also criticizing the Liberals, Mr. Singh took several opportunities to attack Mr. Poilievre over the course of the debate. Though the polls suggest the Liberals have the upper hand, the New Democrats are also at risk of losing seats to Mr. Poilievre – who, Mr. Singh alleged, wants to turn Canada into a country more like America, which Mr. Poilievre insisted was not true.

Though the trade fight with U.S. President Donald Trump is a dominant theme of the election campaign, the day-to-day cost-of-living pressures for Canadians – and who will address them – has run parallel throughout.

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During a section of the debate on that issue, Mr. Carney bore the brunt of attacks as the party leaders also sought to outline their promises to ease the pinch for Canadians. Mr. Poilievre, Mr. Blanchet and Mr. Singh, however, each in their own way argued that the current crisis lies at the feet of the Liberals – and in turn at the feet of Mr. Carney.

Mr. Blanchet said a Liberal government under Mr. Carney would be made up of the same MPs, the same ministers and the same hostilities to Quebec, while Mr. Poilievre accused Mr. Carney of being “just like Justin.”

But all four came under criticism from the moderator, who called it irresponsible that no party had a costing of the promises ready for voters. Mr. Blanchet pointed out that his party has released its platform.

Mr. Carney and Mr. Poilievre promised that theirs were on the way, and Mr. Poilievre said one way he will pay for the things he is promising is through his plan to get more natural resources to market, which he says will raise $70-billion in revenue.

The leaders also debated Quebec City transportation issues, immigration and broader foreign policy.

They all vowed to protect the Quebec language and Mr. Poilievre said he would give the Quebec government new powers over immigration policy. Mr. Carney said he supports a cap on immigration.

The leaders were pressed on Canada’s foreign-aid budgets, and asked what they would cut, with Mr. Poilievre responding first and saying he’d cut aid to China and also to UNRWA, an organization that works in Gaza, a reply that pushed the debate into the war in the Middle East. Mr. Singh said the situation in Gaza amounts to a genocide and challenged Mr. Carney on why he won’t call it that. The Liberal Leader said he won’t politicize the word genocide.

In introducing the topic of U.S. trade tensions, moderator Patrice Roy, a journalist and Radio-Canada news anchor, called the issue the elephant in the room and asked each leader why they are the best person to negotiate with the President.

Mr. Poilievre and Mr. Carney both promised to stand up to Mr. Trump and to focus on boosting economic growth.

Mr. Singh said he would ensure that unemployed workers receive help, while Mr. Blanchet criticized Mr. Carney for lacking political experience.

The opening round on trade and the economy featured civil exchanges in which the party leaders highlighted their key campaign promises. It ended on a lighthearted note after they were asked what U.S. goods they’ve given up in response to Mr. Trump’s tariffs.

Mr. Blanchet and Mr. Singh both listed strawberries and other fruits, while Mr. Carney said wine and other U.S. alcohol. Mr. Poilievre said he makes sure to buy Canadian beef.

While the leaders agreed that Mr. Trump cannot be controlled, Mr. Carney said he has the experience required to work with the President.

“He respects force. He respects people who know how the world works and how the private sector works,” Mr. Carney said.

Mr. Blanchet said Mr. Trump’s policies will be “toxic” for the U.S. economy.

“We need to negotiate in a rational way,” he said.

Mr. Poilievre said responding to Mr. Trump involves expanding Canada’s economy and natural-resource exports.

“No one can control the decisions of Donald Trump. But we can control our domestic economy by reversing the economic policies that the Liberals brought in that weakened our economy,” said Mr. Poilievre.

The moderator pressed Mr. Poilievre on his pledge to keep Radio-Canada but not the CBC, asking how that would be possible given that the French and English services are interconnected.

“It’s possible,” the Conservative Leader said. “The CBC can finance itself with its own revenue as a not-for-profit organization.”

The commission responsible for this week’s debates announced another change Wednesday morning, saying it had revoked the Green Party’s invitation as it no longer met the eligibility criteria.

The federal election campaign kicked off on March 23 and voting day is Monday, April 28. Four days of advance voting begin Friday.

The timing of the French-language debate was moved ahead by two hours so as not to conflict with a key NHL hockey game involving the Montreal Canadiens.

The Canadiens won the game 4-2, securing a spot in the opening round of the Stanley Cup playoffs.

With a report from Emily Haws

Respondents to the Nanos poll were asked: “Of the current federal political party leaders, could you please rank your top two current preferences for Prime Minister?” The full methodology for all surveys can be found at: tgam.ca/polls.