Would like to talk with a Canadian investment banker

Long time lurker, hope this helps...

1. If you want to remain in TO definitely Big 5. Generally speaking, you'll get a better experience than working at one of the globals. Globals can be a toss up in terms of pitch vs. live deal work (same can be said about some of the Big 5 groups, but usually a safer bet). If you wanted to try and lateral to NYC or move to the buyside in the States, then a brand name like GS or Evercore might be more helpful.
2. Deal flow is dependent on the group you're in and typically you'll be busy in any product group across the Big 5. In terms of solid coverage groups, BMO M&M, TD/RBC Diversified, TD CMT are ones that come to mind.
3. Anecdotally, I've heard GS Toronto does a lot of pitching so if you plan on staying in TO, probably better working for the Big 5.
4. Just like most other places comp is pretty comparable across the street.
5. Is this really a consideration? Some banks (i.e. RBC) have an open concept so no one gets an office, but usually Director+.

Feel free to PM me if you have more questions.