Originally Posted by
AA_EXP09
For domestic I have done this (or on hidden city tickets, though that technically isn't a legitimate connection), but I would not advise this for international unless you have NEXUS.
For my DCA/LGA/ORD/MSP-YYZ-Asia/Europe/South America trips on all AC itineraries in the past couple of years, NEXUS has been unnecessary as the quick transit passport/customs form check has been very quick and smooth flowing.
If anything, my issue there is more with longer transits at YYZ than scheduled 60-90 minute ones. If I had more than 4-6 hours of scheduled transit at YYZ, CBSA connections staff would stop me and would tell me to go landside or wait in that boring no-man land without much in the way of any facilities.