I will be traveling out of the country (from US, visiting Canada) for the first time this summer. It's a week long trip for a conference. I'm fairly familiar with how airports work for domestic flights, but customs will add a new wrinkle for me. Mostly, I don't know what to expect.

  - What should I expect in regards to taking my suit-case carry-on vs checking it? E.g. Will baggage claim be before or after customs each direction?
  - How much time should I expect? I have to imagine simple business trips between the US and Canada are pretty routine, but I don't know the routine yet.
  - What should I be aware of regarding purchasing small souvenir items? Picking up some Canadian maple syrup while I'm there seems like a good idea also.

Adding relevant/requested details:

  - Route undetermined, but likely to involve one stop.
  - Probable airports are STL -> ??? -> YUL
  - Obvious intermediate stops are ORD and YYZ