Contrary to your beliefs I think Montreal is quite expensive compared to other cities in Canada. Don't get fooled by price tags. The VAT/GST and PST taxes + MANDATORY TIP (wtf?) is pretty high
But if you are smart, you can file for tax returns each fiscal year and you get some money back(~ $80-100) from govt depending upon your stated income/expenses. 'Good' pizza is pretty expensive too compared to *censored word*ty street stuff and same goes with 'good' restaurants where you actually sit and eat (not Subway/McDs). Spending $100/week is insane too. If you buy groceries and make your own food at home, you can live in $150-200/month comfortably. Be flexible in food. Try Arabic/Lebanese/Chinese cuisine from time to time along with Indian stuff. Rent, as you have stated, is OK. Its not worth for what you pay usually but if you hunt well (the way I have roamed on Montreal streets) you can get a good deal. Renting a studio is pretty bad too. Its more expensive, and boring IMO. Try for new constructions in concrete. They will give you less trouble.
Coming to the point about language, culture and traditions, be prepared for a culture shock if you are from a small town in India/Pak. The metro/NCR guys are well-off as we are used to this stuff day in and day out. Language is predominantly French on my side of the hill (Mount Royal) in and around UdeM, HEC and Poly and English on the other side of the hill (Downtown - McGill and Concordia). I personally find this francophone region better as I see more open spaces, less huge buildings (which I have got bored of) and less desis (gives me an opportunity to improve French, try French cuisine etc) The french which they speak here is pretty much different from the French in France. Its more of a Quebecois accent - harsh and loud (Pardonnez moi Mesdames et Messieurs)
Also, get a bike (aka cycle in India) here. Its almost mandatory if you want to travel, explore and have fun. The metro is not as good as Delhi/Bangalore Metro. Its better than Kolkata Metro though. Buses are definitely better and awesome but rates public transit rates are high as compared to homeland.