I consider myself a Montrealer, a Quebecker, a Canadian and a North-American.
These categories are not mutually exclusive, given that they operate on different levels.
It's like saying "do you consider yourself a male or a human being?". Well, I'm a male, and i'm a human being. One is a subset of the other. Similarly, I consider myself a Montrealer and a Quebecker at the same time because the former is a subset of the latter.
As for separation, I have observed that people in rural areas seem to support sovereignty primarily for historical, linguistic and cultural reasons. People in urban areas (mainly Montreal) tend to take into account ideological considerations as well. This is probably because people who live in urban areas tend to be more progressive, and people who live in suburban or rural areas tend to be more conservative.
It is an interesting mesh of ideas.. we have the left-right political spectrum clashing with the yes-no sovereignty issue. No matter what you believe and what your opinions are, you gotta admit.. Montreal is a fascinating place to live in!