passport stamps for americans leaving canada

I went through Mexico instead of Canada when I traveled to Cuba, but I can tell you that the Canadian authories stamp your passport when you go through immigration after arriving in Toronto. You also go through US immigration and customs at the Toronto airport before you board your flight. Air Canada flights to the US and Havana depart from terminal 1, though you check in for these flights in different zones.

Not that I have the personal experience myself but a lot of friends of mine from the States have avoided Canada for many years…and none have had any problems. It looks like still Cancun is the best gateway

I had good luck asking the immigration officer not to stamp my passport in Montreal. In contrast I experienced a lot of harassment and a secondary inspection upon arrival to Pearson Airport in Toronto (which I would never again use). I have always crossed the US/CAN border by land (where you can still use your BC/DL). If traveling completely by air, it's best to overnight before clearing US Customs for your returning flight (the US Customs Officers in Canadian airports know when the Cuba flights arrive). If traveling completely by air, I would recommend going through Nassau instead (I also had good luck asking that my passport not be stamped there). In any case, the US Customs officers there did not seem very aggressive. I think you would have to go out of your way to call attention to yourself in order to be caught/questioned/flagged (they do not seem to be actively "looking" for illegal Cuba travelers).