Most of the arrests, which police called "a preventive measure," occurred about 1 p.m. at Jean Drapeau Park, an entry point for spectators arriving for the Formula One Grand Prix at the Circuit Gilles-Villeneuve, The (Montreal) Gazette reported.
"The people arrested had objects in their possession which led us to believe that they were on the point of committing criminal acts or violating municipal bylaws," city police Constable Anie Lemieux said.
Those detained were being held near the Biosphere, the American Pavilion on the site where Expo 67 was held, Lemieux said.
Montreal police Inspector Alain Simoneau said there had been threats of an occupation or disruption of the race site by an anti-capitalism group, and officers recognized some people as having taken part in previous demonstrations.
More than 40 people were dispersed from the area, he said. A half-dozen other people also were arrested earlier in the day.
Police used pepper spray to break up a demonstration of fewer than 50 individuals in downtown Montreal, the scene of clashes between police and protesters Saturday night, The Gazette said. It appeared there were several arrests made in that confrontation, the newspaper said.