Five federal party leaders will face off in the first of two official election debates tonight in what may well be their best chance to sway voters before election day on Sept. 20.

With less than two weeks to go, millions of voters are expected to tune in for tonight's two-hour French debate and Thursday's English debate.

Liberal Leader Justin Trudeau, Conservative Leader Erin O'Toole, NDP Leader Jagmeet Singh, Bloc Québécois Leader Yves-François Blanchet and Green Party Leader Annamie Paul will participate in both debates.

People's Party of Canada Leader Maxime Bernier did not meet the criteria established by the independent leaders' debate commission for participation.

Both debates, organized by consortiums of broadcasters, are being held at the Museum of Canadian History in Gatineau, Que., just across the river from Parliament Hill.

The debates come as opinion polls suggest the Liberals and Conservatives are stuck in a tight two-way race, with the NDP and Bloc poised to determine which of the two main parties emerges victorious.

Last week's TVA French debate, to which neither Paul nor Bernier was invited, appears to have done little to move the needle for any party.

In 2019, some 7.5 million Canadians tuned in to the English debate across all traditional and social media platforms while some three million tuned in to the official French debate.

Surveys conducted by the debates commission afterwards suggested that "the debates were central to the electoral process," according to a commission report on the process.

Tonight's French debate, Thursday's English debate pivotal for federal leaders. #ItsOurVote #CdnPoli #Elxn44

"On balance, the debates played an important role in increasing engagement with the issues, leaders, and choices before voters."

That said, the commission reported that its surveys found no measurable difference in intended turnout or change in vote intention between Canadians who watched the debates and those who didn't.

Tonight's French debate begins at 8 p.m. ET.

Topics to be discussed are climate change, the cost of living and public finances, Indigenous Peoples and cultural identity, justice and foreign policy, and health care and the COVID-19 pandemic.

The English debate on Thursday starts at 9 p.m.

The topics for that debate are affordability, climate, COVID-19 recovery, leadership and accountability and reconciliation with Indigenous Peoples.

This report by The Canadian Press was first published Sept. 8, 2021.