In power since 2006, Prime Minister Stephen Harper is seeking a fourth mandate, hoping to hold on to key Conservative support in the western plains and in suburban Toronto.
But the 56-year-old faces stiff opposition from his emboldened rivals.
In one corner is Liberal leader Justin Trudeau, 43, son of former Prime Minister Pierre Trudeau, who is considered the father of modern Canada.
The Liberals have sneaked ahead in the most recent opinion polls.
In the other corner is Thomas Mulcair, 60, head of the New Democratic Party (NDP) and looking to build on a second-place finish in 2011 and govern for the first time.
The social democrats started the campaign - one of the longest in Canadian history - in July as the frontrunner, promising new social spending but no budget deficits or tax rises.
The NDP has also been fighting the chipping away of support by separatist Bloc Quebecois and the Greens.
Polls showed the Liberals gained five percentage points in the past week and now have 35 to 37 per cent support, which would be enough to form a minority Government. Harper stepped up his game recently, attacking the Liberals' economic platform that includes tax rises and deficit spending on new infrastructure and social programmes.
