I bought a Tissot PR50 in 2009 and it recently ran out of batteries. I still had the little booklet that I got that listed official service providers and Helvetia was the only one in Montreal.
I called them on Monday to ask their hours, and they said 9-5 on weekdays. They have moved to suite 109 in the same building. I Went there this Tuesday morning and got the watch battery replaced in 15 minutes. I am happy with the service, the hardest thing was just finding their place.