On a Friday night, at 8:30 PM, there is the Tour de Nuit, which is a 22 km race at night around central Montreal. It starts on Notre Dame Street and finishes at Maisonneuve Park, near the Olympic Stadium. Usually, 12,000 cyclists participate.
The biggest race in on a Sunday morning. It is the Tour de l’île. There are 30,000 racers, going 50 km all around the east end of the island of Montreal. It starts and finishes at Maisonneuve Park, near Metro Pie-IX or Viau.
If you want to participate, you have to register. Check the website for details.
Many streets will be closed for the races. For maps of the closed streets, look in the newspaper or check the website.