Circuit Gilles Villeneuve in Montreal is the track for the Canadian Grand Prix F1 race. It's usually open to cyclists, and when I was there a few years ago I rented one of those horrible Bixi bikes and made a few laps.
Yea the track in Montréal is open to cyclists for most of the season; along with the mountain itself it is one of the two main places in the city where cyclists tend to train.
Circuit Gilles Villeneuve is a fantastic place not just for cycling, but also running and roller-blading. I have been there for a couple of runs - the lanes are clearly demarcated, and the track is a real treat to run on.