You do NOT need to claim baggage in YYZ when travelling inbound US/Intl connecting to Intl. When you walk along the upper arrival corridor, prior to taking the escalator/stairs down into the customs hall, there is a desk manned by 2-3 CBSA agents for transit passengers. It leads directly into the upper international departures corridor. You will still need to fill out a declaration card, but you will be through that check in less than 5 minutes after deplaning your FLL-YYZ flight.