YYZ was the pits for me, loadsa questions that seemed to try and trip me up, then finally he grunted and stamped me through.
It was actually easier getting into Havana, no questions, just a smile and a stamp. (Getting out was harder, just one question :-)
Never did get my *A miles on my UA account for CAN-HAV-CAN :-(
(I was there legally, i)UK Citizen, and ii)as I reside in the US, I was there as a journalist. Absolutely nor problem coming back into the US at CLT, Immigration asked me how long I was in Cancun, "4 hours" I said, said I was in transit from Havana, I had a journalist visa so he was fine, we ended up discussing Castro (I was the only non-US citizen on that flight, nice having 3 inspectors to myself!!).
Customs was just a couple of questions, "Did I have more than $10k?", "No", "have a nice day and welcome back"