One of the people responsible for the Safe Third Country Agreement between Canada and the United States says reducing the number of migrants coming into Canada at irregular crossings isn’t just a question of renegotiating or scrapping the deal, but rather the focus should be on the federal government being able to better control the border.

The irregular border crossing at Roxham Road along the Quebec-New York border has seen a surge in migrants in the last year, and Quebec Premier François Legault has been calling on the federal government to find a solution, while his province struggles to handle the massive increase in people crossing.

Legault’s plea caused a war of words between Prime Minister Justin Trudeau and Conservative Leader Pierre Poilievre this week, when Poilievre waded into the debate, saying “if we are a real country, we have borders. And if this is a real prime minister, he is responsible for those borders.”

Trudeau later responded saying that “if Pierre Poilievre wants to build a wall at Roxham Road, someone could do that. The problem is we have 6,000 kilometres worth of undefended shared border with the United States, and… people will choose to cross elsewhere.”

John Manley — a former deputy prime minister who served under Jean Chretien and one of the signatories of the Safe Third Country Agreement in 2002 — told CTV’s Question Period host Vassy Kapelos, in an interview airing Sunday, he doesn’t think the crux of the problem is whether or not the deal should be modernized or renegotiated.

“I think there's a separate issue there, which is Canada's ability to control its own borders,” Manley said. “I know it's simplistic to say to just block Roxham Road, and the government's right to say, ‘well we do that and they'll just come in somewhere else’. Possibly true.”

“But fundamental to the nation's sovereignty is the ability to control our borders,” he added.

The STCA was first signed 20 years ago, and there have been talks of modernizing it since 2018, with some changes made in 2019. Under the STCA, people seeking refugee status in either Canada or the U.S. must make their claim in the first country they enter.

The agreement applies only to official land border crossings, which means asylum seekers who manage to enter a country via an unofficial crossing — such as Roxham Road — are not returned.

Manley said the nature of the Canada-U.S. border adds challenges: some of the border is over water, much of the border is informal, and in some places, there are even buildings that straddle the line.

“So it's not without its complexity, but nevertheless, it is something that the government has to be able to do, and to say that if we stop this [irregular crossing], they'll come in somewhere else … that's not really the point,” he said.

Legault said this week Trudeau needs to discuss renegotiating the Safe Third Country Agreement with U.S. President Joe Biden when he’s in Ottawa for his first official visit to Canada in March.

But Manley said he’s unsure how those discussions might go, considering the agreement in its first iteration was something Canada pushed for while the United States was reluctant to sign on.

He said post-9/11, there was “quite a large inflow of refugee claimants” from all over the world passing through the U.S. and crossing into Canada to seek asylum. He said they were “very well organized.” The surge in numbers meant Canada couldn’t keep up, so in the time it took to process their applications, they would settle in Canada, and began to cause “quite a strain on social services.”

The number of migrants crossing from Canada into the United States was also a fraction of those going in the other direction, so there was little incentive for the Americans to sign the deal in the first place.

“It is really a question for the Americans,” Manley said. “I can tell you that this was a very difficult agreement to achieve.”

He added: “I think there will be a lot of reluctance on the part of U.S. authorities to give this to Canada without something in return. And I don't know what there might be that we could give in return.”

Manley also said the loophole of irregular land border crossings was never a consideration at the time the agreement was signed.

“The notion that people would come en masse through illegal points of entry seemed unlikely at the time,” he explained. “It just wasn't a factor. We didn't really expect it to become one and indeed, it didn't become one for quite a long time.”

He said the number of refugees in the world “breaks your heart,” and that Canada has a “responsibility as a wealthy country” to welcome them, but “we should choose them, and they should come in on a manner in which we provide for their support.”

“The federal government has some responsibility because of its control of the borders to do that,” he added. “We shouldn't be leaving cities and provinces stranded because of an uncontrolled flow of people coming in claiming to be refugees.”

With files from CTVNews.ca’s Senior Digital Parliamentary Reporter Rachel Aiello