Thank you!

As many other transit authorities, the STM [0] offers "GTFS" data (a standard feed format for transit info) [1].

Mucking around STM's public site, you'll also see the schedule information go by if you inspect the network requests. From what I've seen, their API endpoints are stable, reliable and fast. I've had to do ~2 updates in >1 year of service.

[0] http://stm.info/en [1] http://www.stm.info/en/about/developers

[ edit: that rumor is just a rumor :-) ]