Justin Trudeau will on Wednesday officially kick off what is set to be a grueling campaign for a second term as he takes on surging rivals in Canada’s October 21 national elections.

The prime minister is due to meet Governor General Julie Payette at 10am Ottawa time (10pm Hong Kong time) and ask her to dissolve parliament.

The election campaign can then officially begin, although political leaders and parties have already been wooing voters with pre-election ads, announcements and whistle stops in key battlegrounds across the country.

Elected in 2015, Trudeau and the Liberal Party will be battling to hold onto a majority in parliament against untested rivals Andrew Scheer of the Conservatives and New Democratic Party leader Jagmeet Singh, as well as the strengthening Greens led by Elizabeth May.

Voters will choose all 338 members of the House of Commons, with the latest poll on Tuesday showing the Liberals reclaiming a slight lead over the Tories.

Accusations of Trudeau meddling in a criminal prosecution sent the Liberals’ popularity tumbling at the start of the year.

Climate change and affordability are widely predicted to be the main issues in the campaign.

The Canadian economy is strong, posting second-quarter growth of 3.7 per cent and almost half a million new jobs created in the last year.

But the economic gains have not been widely felt, and Canadians have increasingly expressed concern about a rising cost of living. (AFP)