Votes are being counted on Monday in a Canadian election that will choose a leader to confront US President Donald Trump's trade war and annexation threats, which he renewed in an election day message.

The Liberal Party, led by new Prime Minister Mark Carney, was trailing Pierre Poilievre's Conservatives until Trump's attacks on Canada sparked a wave of patriotism and a sudden reversal in poll forecasts.

Polling stations across the vast country that spans six time zones have started to close, with results from smaller eastern provinces trickling in.

Voting was ongoing across much of Canada and a projected outcome is not expected until later on Monday.

Trump inserted himself into the race early in the day with a social media post saying Canada would face "ZERO TARIFFS" if it "becomes the cherished 51st state."

Poilievre, criticised during the campaign for his at-times muted anger towards Trump, hit back firmly.

"President Trump, stay out of our election," he posted on X. "Canada will always be proud, sovereign and independent and we will NEVER be the 51st state."

Carney also weighed in, saying on X: "This is Canada and we decide what happens here."

The 60-year-old has never held elected office and only replaced Justin Trudeau as prime minister last month.

Public broadcaster CBC's poll aggregator's final update late Sunday put the Liberals' national support at 42.8 percent, with the Conservatives at 39.2 percent.

The performance of two smaller parties - the left-wing New Democratic Party and the separatist Bloc Quebecois - could be decisive as strong showings by both parties in past votes have curbed Liberal seat tallies.

Nearly 29 million of Canada's 41 million people are eligible to vote in the massive G7 country. A record 7.3 million people cast advanced ballots.

Canadians will elect 343 members of parliament, meaning 172 seats are needed for a majority. The Liberals won a majority in 2015 but have governed with a minority since 2019. (AFP)