MISSISSAUGA, Ont. -- Liberal Leader Justin Trudeau took aim at conservative premiers Friday, dangling $1 billion for provinces that choose to implement vaccine passport systems and a direct call for Ontario Premier Doug Ford to take the offer.

Only Quebec and British Columbia have moved on vaccine passports at a provincial level, with Quebec implementing them next week and B.C. in mid-September. Manitoba is expected to announce details on a vaccine passport there shortly.

Trudeau thanked B.C. Premier John Horgan and Quebec Premier Francois Legault for their plans, noting strong uptakes in vaccinations after their respective announcements, before setting his sights on Ford.

"Already, Premier Horgan and Premier Legault have stepped up," Trudeau said during a stop at a restaurant in Mississauga, Ont. "I certainly hope that here in Ontario, Premier Ford steps up, too. It's time for him to listen to public health officials."

It sounds like he will.

Three senior government sources with knowledge of the situation told The Canadian Press on Friday that a plan for a system is in the works, with details being worked out.

The issue is not without some controversy.Across the strip mall parking lot from where Trudeau spoke, a sign hung on a chiropractor's office labelling the prime minister a "commie" and added, "No passports," hinting at the protesters who decried the vaccine passport policy when the Liberal leader arrived and departed.

Ontario's premier had found himself at odds with local public health officials who say they're considering regional vaccine certificates in the face of Ford's refusal to implement a provincewide proof-of-vaccination system.

Trudeau has largely avoided campaigning against Ford so far in this election, after the 2019 campaign focused heavily on the premier of Canada's most populous province.

Ford's office has also stayed out of the federal election this time.

But polls have suggested the race both nationally and in Ontario is tightening between the Liberals and Conservatives, and strategists said the 2019 plan to go after Ford heavily in Ontario helped the Liberals federally.

Ford spokeswoman Ivana Yelich said in a statement that the provincial government has already outlined "far-ranging mandatory vaccination policies for high-risk settings in the country." She added that the province will "respond accordingly" to the trajectory of case counts and the more virulent Delta variant.

Trudeau has decided that vaccine mandates can be a key wedge issue against the federal Conservatives, taking shots Friday at Conservative Leader Erin O'Toole in his prepared remarks, trying to contrast the two views.

In particular, Trudeau has gone after O'Toole for not requiring all Conservative candidates to be vaccinated. Trudeau said Friday that not all Liberal candidates are fully vaccinated but would be soon.

Raucous protesters, opposed to various pandemic policies, have greeted Trudeau at many stops on the campaign trail. In Nobleton, Ont., on Friday, a chaotic scene developed during a photo-op in a bakery, where several unmasked demonstrators managed to get inside.

One young mother, holding a baby in one arm and shooting video on her phone in the other, accused Trudeau of "attacking" children and "funding segregation." At least one protester was removed from the building.

Dozens of demonstrators gathered outside the Liberal leader's next stop in Bolton, Ont., where they chanted obscenities at Trudeau.

Trudeau cancelled his evening rally over a security threat Friday and later held a media availability in Brampton, Ont., saying he's never seen such intense anger while on the campaign trail.

"I think this is something that Canadians, all of us, need to reflect on because it's not who we are," he said.

"We are a country that is comfortable with differences, we have to listen to each other."

Dr. Katharine Smart, a Yukon pediatrician and president of the Canadian Medical Association, said federal parties shouldn't be divided on the use of vaccine passports or certificates, saying it "needs to happen from the perspective of science" to combat the pandemic.

It would be helpful for the federal government to step up and offer all provinces passport systems that are already working, she said.

"We're in an emergency and we've got everyone kind of walking their own path here, with tools that we know everyone needs, and they need the same tool," Smart said. "So why don't we do it one way properly, that works, and have everyone be consistent?"

Trudeau has previously said Ottawa will enforce vaccinations for federal civil servants and federally regulated industries including airlines and banks.

On Friday, he said that a proof-of-vaccination system for local businesses is the domain of provinces that hold details on the vaccination status of residents.

The proposed funding would be on a per-capita basis and only if provinces back their systems with "an enforceable mandate" to show proof of full vaccination for visiting non-essential businesses.

"I want to remove the barrier that is, 'Oh, it might be really expensive to do,' from provinces' calculations," Trudeau said, surrounded by journalists, staffers and restaurant workers standing in tight quarters.

Trudeau also promised a re-elected Liberal government would put $100 million toward researching the long-term effects of COVID-19.

This story by The Canadian Press was first published Aug. 27, 2021.

-- With files from Mia Rabson and Holly McKenzie-Sutter