hey slybry,
i'm sure there are few of those in montreal. i have not been underneath e46 and after, yet, but looked after couple of e36 and e30 before. it is little different servicing bmw's, but as long as the technician is patient and takes his time, normal things like oil changes (what else does e90 need, really?) can be done anywhere.
i've read that e90's oil does really last long time so you may be worried over nothing.
if you have a great mechanic, i would just talk to him, ask him to take his time, tip him couple of extra bucks and bring your own oil. (cause he may not stock bmw spec oil, and he may also need to buy torx bits).