Canadians have voted in general elections marked by a strong desire for change with Liberal leader Justin Trudeau, the son of a former prime minister, tipped to end nine years of Tory rule.

Public opinion has swung wildly during the hard-fought campaign, but final polling showed the Liberals eight points ahead of prime minister Stephen Harper's Conservatives.

Enthusiastic crowds packed campaign rallies over the weekend, as leaders criss-crossed a nation covering 10 million square kilometres in a last-gasp push to win over undecided voters.

At a stop in Calgary on Sunday, Mr Trudeau said the Liberals offered "not just a change in government, but a better government".

The 43-year-old, who made a late surge from third place, is the eldest son of Pierre Trudeau, considered the father of modern Canada.

He is hoping for a repeat of the "Trudeaumania" that swept his late father to power in 1968, replacing the plodding management style of the old guard with a bullish vision and flare that Canadians were craving.

Mr Trudeau's wife and three young children accompanied him to a polling station in Montreal on Monday, while Mr Harper and his wife cast ballots in Calgary.

Harper popularity at all-time low

For many Canadians, the election has become a referendum on Mr Harper's stiff management style, as well as who would be best to replace him.

In power since 2006, Harper is seeking a fourth mandate, hoping to hold on to key Tory support in the western plains and in the suburbs of Toronto, Canada's largest city.

But he is now up against a powerful desire for a change in leadership and his personal image has fallen to an all-time low — highlighted by Tory television spots that open with a stark acknowledgment: "Stephen Harper may not be perfect...".

Over the past nine years, Mr Harper has led two minority governments and one majority government, under mandates that have never exceeded 40 per cent of the popular vote.

The incumbent warned Canadians would pay more taxes under a New Democratic Party (NDP) or Liberal government, and see Canada plunged back into deficit.

"Every single vote for a Conservative candidate is a vote to protect our economy against Liberal and NDP deficits and taxes," Mr Harper said.

The NDP, led by Thomas Mulcair, hoped to build on its second-place finish in the last ballot, in 2011, and govern for the first time ever.

"Canadians deserve change in Ottawa," Mr Mulcair told a crowd in Toronto on Sunday.

"Let's remember that it was Liberal arrogance and corruption that Stephen Harper promised to clean up and, today, after 10 years of Conservative scandals, the Liberals are asking you to trust them to clean up that mess."

But the NDP stumbled in recent weeks, losing key support in Quebec province over its opposition to a popular ban on the niqab worn by Muslim women.

Campaign one of longest in Canadian history

Nanos polling showed the Liberals have 38.2 per cent support versus 30.1 per cent for the Tories, while the NDP sank to 21.2 per cent. The margin of error is 2.2 percentage points.

Despite a cold snap in parts of the country, officials were expecting a big turnout with 26.4 million people registered to vote in 338 electoral districts.

Results could be known as soon as polls close in central Canada, and half an hour before the last poll closes in the westernmost part of the country.

The 11-week campaign was one of the longest in Canadian history, giving voters unprecedented exposure to the party leaders and their ideas in five debates and almost daily stump speeches.

Along the bruising way was debate on how Canada should handle a record influx of people fleeing war in Syria, a court ruling quashing a ban on the niqab and a recession — crises that gave Canadians a chance to assess parties' reactions in near-real time.

AFP