Originally Posted by Spounce

2 hours is plenty of time. If you arrive YYZ from the USA on AC, UA or US, you'll arrive at Terminal 1. AC's flight to GRU departs from the same terminal.

Upon arrival at YYZ, you'll see signs for CUSTOMS A and CUSTOMS B. CUSTOMS B is an immigration checkpoint for those who are connecting to an international flight. Clearing immigration at CUSTOMS B usually takes 5 minutes or less. You'll be at the gate for your GRU departure within 10 minutes of leaving CUSTOMS B. Checked bags, if you have them, don't need to be picked up.

If you return GRU-MSP via YYZ the procedure will differ since you'll pre-clear US customs before boarding your YYZ-MSP flight.