On this trips pairing we were to fly to YYZ and DH back(on that exact same plane). When we landed they came onto the plane and said since we weren't the crew actually flying the plane back that we would have to clear customs. I argued it was ridiculous that we had to go through customs without ever having left the plane but they didn't seem to care. We had to go through Canadian customs, go to the ticket counters to get our tickets, then through American customs, then through security, all the way back to our gate, just to have zero paperwork to show for it because they took everything from us as we went through the checkpoints. It was crazy. Our company only had us scheduled for 15min turn but it took about 45-50min. We even managed to cut in front of all the other crews at the Canadian customs. On the way back the American customs said since we weren't there over 90 minutes they didn't care.

Next time we won't tell them anything and just grab a seat in the back. With the size of that terminal we covered some serious ground.