In the last hours of the campaign, unusually held in the depths of Canada's savage winter, party leaders criss-crossed the vast country to shore up support and convince still undecided voters.
Mr Harper, his party running 10 points ahead of Prime Minister Paul Martin and his scandal-tainted Liberals in opinion polls, basked in the glow of an apparently imminent victory as Martin staged a last ditch bid to stave off defeat.
"We can win because it is time for a change, time to move forward, time to get beyond the scandals and investigations and corruption," Mr Harper told a cheering crowd in the frigid central city of Winnipeg Sunday.
"Let the Liberals claim, for Canada, this is as good as it gets. I know for our Canada, the best is yet to come," he said, chastising his main opponents as a "disorganised, directionless and desperate government."
Mr Martin, a millionaire former shipping tycoon, who claims Mr Harper is an "extremist" in the mould of US arch-conservatives, however refused to admit defeat.
"We will win!" he promised cheering supporters at a rally in Richmond, a suburb of the western city of Vancouver.
"We have the numbers. We can stop Stephen Harper. We can elect a government that reflects the Canada we believe in. It is up to us. So I am asking (you) to dig deeper, go further, to fight harder."
A poll by Strategic Counsel for CTV television and the Globe and Mail newspaper on Sunday gave the Conservatives 37 percent of the likely vote, and the Liberals 27 percent.
Those figures, in line with other polls, would translate to a solid victory for Mr Harper, but hand him a minority government, forcing him to piece together a coalition administration with help of the separatist Bloc Quebecois or the left-wing New Democratic Party.
The New Democrats had 18 percent in the CTV poll, with significant gains in west coast British Columbia, and in Toronto, Canada's economic hub.
The Bloc, which only fields candidates in the French-speaking province of Quebec, was at 11 percent.
In vote-rich Ontario, a bastion of liberalism, the race seemed to be tightening in the final hours with the Conservatives tied with the Liberals at 37 percent.
The Montreal newspaper La Presse carried an Ekos survey which predicted the Conservatives would win 120 to 130 seats in the 308-seat House of Commons.
Sullied by corruption allegations, the Liberals are no longer the political machine which bulldozed to four straight election victories, three under retired ex-prime minister Jean Chretien.
They have barely clung to power since voters, tired of a patronage scandal, snatched away their ruling majority in the last election in June 2004.
Mr Harper told CTV television on Sunday that he would "try and have something for everybody" in Canada, promising reduced taxes and a crackdown on crime, rejecting claims he was an extremist.
"I am a conservative, I believe in the power of free markets and
liberalised trade and making sure Canada's economy is dynamic."
"I also believe you need social services but you should deliver them in a way that empowers people, these are all small 'c' conservative views."
Liberals claim Mr Harper would threaten abortion rights, revisit a law permitting same-sex marriage passed by Martin in 2005, and renege on Canada's Kyoto Protocol commitment to combat global warming.
The Conservative leader may also review Canada's refusal to join the US anti-ballistic missile shield.
Mr Harper has, however, softened a once cold, angry image and portrayed himself as a reassuring prime minister-in-waiting.
Twenty-three million Canadians are eligible to vote in Monday's election, across six time zones.