Hi Alex,
I lived in Montreal from 86' to 96' , in those days, I made a living mostly as a live sound guy. These days, I do mastering as my secondary income, with some mixing gigs.
I now live 220 kilometers from Montreal, but most of my work comes from either Montreal or Quebec city.
Montreal as at least 4 serious Mastering house, and there are possibly 6 high end studios and hundreds of mid to low level places. Right now things are really tuff there. Studio Morin Heights which in the 80's did Rush, The Police, Bowie, ect. as recently shut down, as well as many other top of the line places.
Severe budget cuts from the labels are forcing the downward trend here too. If you are considering Montreal, you better set up your own shop, as no one is hiring anymore. And even then, unless you can have your own stable of artists, you probably won't make it.
At the higher echalon, the hierchy is well established with no room to get in.
Good luck to you,
Oldfart
PS you better be prepared to freeze in the winter !!!