The man, whose name officials did not release, was removed from the plane at Pierre Elliott Trudeau International Airport and arrested, said Lauren Gaches, a spokeswoman for the Transportation Security Administration.
Other passengers on Aeromexico Flight 006 from Charles De Gaulle Airport to Mexico City International Airport were re-screened and allowed to re-board the flight, Gaches said.
As a matter of policy, the TSA does not confirm or deny whether a person appears on a government watch list.
"The United States' ability to refuse entry into its territory of any flight it deems to present a threat to its security is recognized by numerous countries and is consistent with international agreements," Gaches said.
Montreal airport official Marie-Claude Desgagnes said the plane was allowed to take off shortly after 10 p.m. EDT. It was expected to arrive in Mexico City about 3:30 a.m. EDT.
TSA referred questions to Aeromexico and Canadian authorities.
A spokesman for Canada Border Services, Dominque McNeely, said there was not an incident on the aircraft and that law-enforcement officials boarded the plane around 2:30 p.m. and took the suspect into custody.
"The flight landed and we had excellent cooperation with everyone involved," he said.
McNeely said the man was being detained in Montreal and a detention hearing would be held within the next 48 hours.
A Royal Canadian Mounted Police official said officers assisted Canada Border Services but declined to provide further details.
In Mexico City, a woman who answered the phone at Aeromexico late Sunday said no one was available to talk to the news media.