Your understanding is 100% correct (can't write anything more than that) If going back the same way, however, you'll clear US immigration in Seattle, then collect and re-check your luggage at the designated counter after customs.


Just 7 days ago from the time of posting this @TorontoPearson tweeted: Customs open at 3:30 am and counters are open 3 hours prior to scheduled flight times. Hope this helps. Regards. Therefore, the hours you listed are out of date.

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