A question about the looming referendum on Scottish independence came up Wednesday as Harper took part in a question-and-answer session in front of a business audience in London.
Recent public opinion surveys in Britain show the Yes and No sides are almost evenly split with a little more than two weeks left before the Sept. 18 vote.
The gap between the two sides has been narrowing for the last month, with some 42 per cent of poll respondents saying they would vote in favour and 48 per cent standing opposed, according to a poll tracker in The Telegraph newspaper.
Harper rhymed off a host of global woes — from terrorism and trade to Ebola outbreak and climate change — and questioned how facing those challenges would be better in a fractured country.
It is a conundrum that Canadians faced for more than four decades with the separatist movement in Quebec, culminating a period of reflection that followed the close call of the 1995 referendum.
"What would the division of a country like Canada — or the division of a country like the United Kingdom — do to advance solutions to any of those issues?" Harper asked in response to a question by Fraser Nelson, the editor of weekly conservative magazine The Spectator.
"We like to think in Canada that our country is a strong and positive force in the world. And we think from the Canadian perspective that a strong and United Kingdom is an overwhelmingly positive force in the world."
Nelson joked that maybe the Canadian prime minister should stick around and take his message up north, to which Harper conceded the sentiment might not be well received in Scotland.
He underlined that ultimately it is "a decision for the Scots," one that should be respected, regardless of the outcome.
"This is a vote with immense consequences and those consequences should be thoroughly understood and digested. And the public, particularly the establishment should be more than willing to accept the judgment of that ordinary people, rightly or wrongly, deliver," he said.
"I don't think there's any way of softpedalling that. It's momentous and should be treated as such by all sides.
Canadians have trouble relating to the notion of a divided Britain because the English and Scottish cultures have been so thoroughly integrated in North America, Harper said.
But where they do understand the current dilemma is through the lens of the country's experience with Quebec.
"That debate has gone on and it went on intensely for very a long time," he said. "Ultimately that intense debate did not create — for a long, long time — any kind of clear winner. It created a society that was very divided."
Harper suggested the notion of Quebec independence has faded from the public discourse because a younger generation has asked itself the question how it relates to "things that actually matter in my life," such as the economy and jobs.