Originally Posted by mcgahat
The way I read it Visit and Transit was the same process, I have never transited via Canada so cant say for sure but you still need to go through immigration like everyone else. When you enter Canada from the the US you are harassed by Canadian immigrationa (at least suspicious folks such as me are) and when you enter the US from Canada you are harrased by US immigration.
Canada's visa process is a lot easier for various non-VWP country citizens than the U.S.'s. The U.S. also has a USD100 non-refundable visa application fee which you lose if your transit visa application is rejected. I believe you also need your ticket in hand so if you buy a non-refundable and the visa is rejected, you can end up losing a lot of money.
That said, YVR has sterile transit at least for U.S.-int'l and you can bypass Canadian immigration for int'l-U.S. (to go straight to U.S. pre-clearance). I don't know about whether int'l-int'l sterile transit is available (as very few flights would make sense).
YUL has sterile transit at least for passengers travelling between St. Pierre and CDG.
Not sure what YYZ has or will have (when the AC terminal is rebuilt).