It wasn’t his central campaign theme, but prime-minister-designate Justin Trudeau now has a window of opportunity to surprise the country with a big climate-change deal – not the one in Paris, but the one with the premiers, where the rubber really hits the road.

That would be a potent political symbol for a leader who promised change. Over nine years of Stephen Harper’s rule, Canadians got used to the idea that action on climate change is distant or elusive.

Mr. Trudeau can go to global climate-change talks Paris in December and promise Canada will take real action to reduce emissions, and win a round of global applause.

The real political surprise is that he has a shot at striking a deal within Canada, with the premiers, in the months that follow Paris, to create a plausible path to actually meeting targets. That’s a surprise because climate change wasn’t at the heart of his campaign. Mr. Trudeau declined to set emissions targets, or spell out details of a pledge to set a price on carbon.

But it turns out his platform was shrewdly constructed to facilitate a deal with the provinces once in office.

That matters because under Mr. Harper’s tenure, some provinces acted. British Columbia instituted a carbon tax, while Quebec entered a cap-and-trade system with California; Ontario announced it will join, too. Provinces don’t want the federal government overturning all that. And a national plan depends on getting all provinces in, notably Alberta.

There’s unusual political will among premiers. Ontario’s Kathleen Wynne and Quebec’s Philippe Couillard have touted climate co-operation, and now there’s an Alberta premier, Rachel Notley, promising meaningful action.

“The ground is well set for them to actually make some progress,” said David McLaughlin, former CEO of the defunct National Round Table on the Environment and the Economy, a former senior New Brunswick civil servant and chief of staff to former PM Brian Mulroney and finance minister Jim Flaherty. “They’re prepared to say, ‘Yeah,’” Mr. McLaughlin said. “But it’s also, ‘Yeah, but …’”

There are huge differences between the provinces. Quebec has hydroelectricity and has committed to cut emissions to 37.5 per cent below 1990 levels by 2030. Alberta has a resource-driven economy and has pledged emissions will peak in 2020 – but hasn’t yet said what happens then.

And Saskatchewan’s Brad Wall is not gung-ho: He said he plans to go to Paris to make sure Mr. Trudeau doesn’t commit to something that will “kneecap” the province’s economy.

But Mr. Trudeau will not be under pressure in Paris. The draft agreement allows for different national targets, and after just weeks in power, he won’t be expected to best the target set by Mr. Harper of reducing Canada’s emissions to 30 per cent below 2005 levels by 2030.

In fact, the Liberal platform said he wouldn’t set new targets until there’s a federal-provincial plan, and promised a first ministers’ meeting within 90 days of Paris. Provincial sources say with the premiers present, the deal-making will begin in Paris.

That’s the hard part. Mr. Trudeau will have to negotiate a national standard among disparate provinces. But what kind?

Alberta won’t set the same deep emissions-cut targets as Quebec or Ontario. A deal could instead require all to set a comparable price on carbon. But B.C. already has a $30-per-tonne tax, and Quebec has a cap-and-trade system where the price is $12 to $15 per tonne of carbon dioxide, and will fluctuate.

And how does Ottawa enforce a deal? It could tax carbon in provinces that don’t have their own tax or cap-and-trade system, but that would appear heavy-handed. Or it could also promise money to provinces that agree to green initiatives or meet targets.

As it happens, the Liberal platform is full of funding promises that could be used to smooth a deal: $6-billion over four years in “green infrastructure” funding, $2-billion to endow a Low Carbon Economy Trust and hundreds of millions for green-technology initiatives.

Mr. Trudeau’s platform, vague on targets and details, allows flexibility to negotiate with premiers – and pockets of money to aid a deal – at a time when there’s political will at the premiers’ table. After saying little about it in the campaign, Mr. Trudeau arrives in power with an opportunity to make a climate deal.