Under Canada's new fixed-date election rules, the campaign can only run a maximum of 50 days. A majority government requires a single party to win at least 170 seats.
Trudeau won a majority government in 2015 with 184 of the 338 seats in the House of Commons. The Conservative Party got 99 and the New Democratic Party (NDP) had 44 while the Bloc Quebecois had 10 and the Green Party got one.
Several other MPs were also sitting as Independents, including Jody Wilson-Raybould and Jane Philpott, who were forced out of caucus by Trudeau for raising concerns about the SNC-Lavalin scandal. Both are running as Independent candidates in this election.
The Conservatives also lost Maxime Bernier, who was elected under their banner but quit to start the People's Party of Canada.
The Greens have seen a surge in popularity in recent provincial elections and federal by-elections, the NDP under leader Jagmeet Singh has plummeted in the polls and heads into the campaign having lost one-third of its incumbent MPs, who opted not to seek re-election.
The official debates of the major party leaders are set to take place on October 7 in English and October 10 in French.
Trudeau's Liberals are seeking a second mandate and will spend the next 40 days pitching Canadians on the party's accomplishments while trying to contrast themselves on social issues with their main rivals.
The latest Nanos poll shows that the Liberal Party has a slight lead heading into the campaign with 34.6 per cent in the polls. The Conservative Party is sitting at 30.7 per cent, the NDP at 16.6 per cent, Greens at 11 percent, the Bloc Quebecois at 4 per cent, and the People's Party at 1 per cent.