Actually leaving from Toronto we went through US Customs in Toronto, same as when I went to WDW last January.
When you land in Orlando you do not go through Customs again, you pick up your luggage, or if using ME they will do it for you.
This is part of the Happiest Celebration on Earth service.
Last year, the transfers to and fro where provided by Mears, and similar to this year, you went to a counter, got a voucher and got on a bus.
Upon leaving your resort you called ahead and they picked you up, same as this year.
The ME service is still Mears, it is just that the buses are decorated.
Obviously there were others without reservations as the line at the aiport was at least 100 peolple ling if not more !