I have a nice 80mm Mamiya TLR lens, black, in excellent shape
(glass is pristine, blades are clean) but the speeds are off even after 'exercising'
the shutter quite a bit. Did anyone knows a reputable repair shop
in Eastern Canada?
There's Canadian Camera Service in Ottawa 613-238-4892. They're OK; the main advantage is that they're in town. Everyone else sends out to Toronto. All will charge around $200 CDN for a CLA of a TLR lens b/c of the integrated shutter.
I would recommend Carol Miller at Flutot's Camera Repair in California; the CLAC (extra c for check) should cost around $50-60 US not including mail. She does "shutter" CLACs and cleaning up the lens is part of the process. You'll have to wait, of course.
There's gotta be a repair tech in Montreal, but if you're going to mail out your lens and want to keep it within Canada to avoid potential customs issues, I highly recommend Dead Link Removed in Hamilton. The owner/tech, Roger, has done a great job on my old Rolleis and Mamiyas.