Re: Can Canada sue?
Nations cannot sue other nations. Still, it does seem quite stupid to conduct immigration/customs checks on someone who doesn't leave the airport.
Many years ago ('93 or '94), I went from New York to Berlin via London (Heathrow). Self-contained terminal, in a security zone - and we were all forced to *leave* the secured zone, and go back through X-ray and baggage scan. Not Customs, at least. Just seemed moronic to take people who go OFF of an aircraft, after being scanned and cleared in a nation even more paranoid than you are yourself, and herd them through - knowing full well the entire time that every single one of those people had a connecting flight to catch. And my belt's metal inlays had set off the metal detectors in the US, but not at Heathrow, thus the unnecessary search was also less thorough, which made it more irksome.
I did make my connection, barely - which of course then pushed back from the gate and sat on the apron wasting fuel for 90 minutes for no apparent reason.