The Canadian government says it is managing the influx of illegal crossings according to Canadian and international law.

“Trying to slip across the border in this way is against the law and not a ‘free ticket’ into Canada,” Hursh Jaswal, special assistant in the office of the minister of immigration, refugees and citizenship, said in an email. “There are rigorous immigration and customs rules to be followed, and make no mistake, we enforce them to safeguard our communities against security risks.”

He added that the agreement “remains an important tool for Canada and the U.S. to work together on the orderly handling of refugee claims made in our countries.”

More than 4,300 asylum seekers have crossed unofficially into Canada since the beginning of the year, according to government statistics. Over 3,300 of them have crossed in Quebec.

The people who cross at unofficial points of entry like the border with Quebec are arrested by law-enforcement officers and checked for security risks before being given temporary papers and scheduled for refugee claim hearings, immigration officials said.

Around 90 percent of the recent arrivals are Haitians, said Ms. Dupuis of the Quebec agency, Praida, that handles new arrivals. Most go to Montreal, which is home to a large Haitian community.

“They are telling us they’re very uncomfortable staying in the U.S. because they think they will never become legal,” Ms. Dupuis said. “Is this a fear justified? We don’t know.”