Originally Posted by
TechnoTourist
Any interaction with US CBP is done at the entry to the pre-clearance area. Once you are past that point you are effectively on US soil and must pass Canadian immigration to exit the airport.
Correct in YYZ T1. Incorrect in YYZ T3. This is only true when (like T1 YYZ) some passengers have connected from international flights without being formally admitted to Canada. Many times at YYZ T3 my flight has been cancelled or I took a VDB or I missed it or I just didn’t want to fly and I was escorted out but never had to redo Canada Customs.