You will have to claim your bags (most likely clear Can customs) and then preclear U.S. entry. That may depend on airline too (may not have to reclaim bags if flying on Air Canada). Which airlines are you flying? Make may a difference as to whether you have to change terminals too or not. 3hrs should be enough time but don't take your time until you get past security and nearly at the gate for your flight to PVD.

As for the return flight, being checked in an hour before hand should be enough time but allow time for lines.