Friendly old Canada, left for dead after nine years of stern rule under the divisive government of the Conservative prime minister Stephen Harper, has returned with a vengeance after voters overwhelmingly turned to a charismatic Liberal named Trudeau in a bid to recapture the glory days that characterized his father’s long and memorable rule.

“Sunny ways!” a hoarse Justin Trudeau exulted as he accepted his striking victory in Canada’s 42nd general election. “This is what positive politics can do.”

The Liberal party’s resounding victory proved that “a positive, optimistic, hopeful vision of public life isn’t a naive dream”, said Trudeau. “It can be a powerful force for change.”

Once mercilessly derided as “just not ready” for the job in persistent Conservative attacks ads, the former drama teacher performed flawlessly throughout the campaign, demonstrating a true populist ease with voters while his party posted videos of the handsome leader sparring with his shirt off or paddling a canoe on a misty river in the manner of his father, the former Canadian prime minister Pierre Trudeau.

Over the course of a 78-day campaign, Trudeau led his party from last place in the polls to a resounding victory, winning 184 seats in the 338-seat House of Commons, according to unofficial results, and the right to form a majority government.

Equally impressive, he won the victory four years after the former Liberal leader Michael Ignatieff suffered the worst defeat in party history. That loss led many to question whether the centrist Liberals could even survive as the leftwing New Democratic party rose to fill the vacant space as the official party of opposition.

But by the end of Monday night, Trudeau’s winnings included the heads of both his major rivals, Conservative leader Stephen Harper, and the NDP’s Tom Mulcair. For a campaign that remained relentlessly upbeat and scornful of what Trudeau called “the politics of fear and division”, the result was exceptionally bloody.

It was the NDP that suffered most at Trudeau’s hands. The party that entered the campaign leading the polls ended it by losing all but 42 of the 95 seats it held in the last parliament, returning to its traditional third-party status.

The Conservative party avoided a similar collapse, retaining more than 100 seats and its dominance in western Canada, but Harper likewise stood down from his party’s leadership. The outgoing prime minister seemed uncharacteristically relaxed and happy as he relinquished power in the face of what he called “a result we accept without hesitation”. But he didn’t actually use the word “resignation” once in his concession speech – the announcement was left to a statement from his party which was circulated to reporters.

The election’s unambiguous outcome did forestall widespread concerns that a closer result could have pitched Canada into a constitutional crisis as various parties wrestled for control of parliament. In the event, the Liberals will enjoy ample time to form a government without the need to seek partners – or even the slightest fear of effective opposition from its suddenly leaderless rivals.

The new Canadian leader’s easiest job will be showing the world that Canada has returned to its traditional role of international boy scout, abjuring the hard-right, militaristic and climate-denying record of the Harper government. In that, he will be helped by the fact that the previous government – despite its own rhetoric and that of its enemies – never completely abandoned the role.

Canadians and international observers can expect a sharp change in tone if not policy with respect to refugees and Canada’s involvement in the Middle East. In his victory speech, Trudeau also took pains to disavow the previous government’s attempts to win votes by inspiring fear of Muslim women who cover their faces.

“We know that our enviable, inclusive society didn’t happen by accident, and won’t continue without effort,” he declared.

The substance of the new leader’s claims will quickly be tested on the international stage at next month’s Paris climate summit, where a hastily assembled Canadian delegation will struggle to shake off the country’s reputation as a laggard in the international fight against climate change.

That may be more difficult than imagined, given Trudeau’s consistent support for the Canadian oil industry, especially the notoriously dirty tar sands. The emerging Liberal juggernaut suffered a minor but telling setback in the final week of the campaign when its co-chairman, Dan Gagnier, was forced to resign after the leak of an email that showed him plotting with the oil industry to influence a prospective Trudeau government.

During his two years in opposition, Trudeau often found himself in agreement with the Harper government, supporting both the government’s law banning what it called “barbaric cultural practices” as well as its sweeping anti-terrorism legislation, which has been widely condemned by civil libertarians. But Canadians were more concerned about the country’s faltering economy, and Trudeau won support by promising a major program of infrastructure spending despite its effects on the government’s fiscal position.

With that, the Liberals neatly outflanked the formerly leftist NDP, which had promised orthodox fiscal rectitude in order to persuade Canadians of their fitness for office.

But all such details were lost in the feel-good atmosphere of the overthrow, with the new prime minister promising a radical reversal of all that was “negative and divisive” during his predecessor’s decades-long rule.

In the last days of the campaign, Harper complained that Trudeau’s platform was “all unicorns and rainbows”.

But it turned out that Canadians are just fine with that.