Great question — answering as the UphillTech team:
I'd like to take an 87-day trip to the USA under ESTA, then travel to Canada for 2 months and return home with a flight to Paris, France. In this situation, are the two months spent in Canada included in the ESTA days count? No. Why would they? Canada is not (yet...) part of the US. Your departure into Canada should have been recorded when you crossed the Canadian immigration checks. You can confirm this at the CBP travel history search tool .
Full answer by oh whatever: https://travel.stackexchange.com/a/195000 (CC BY-SA 4.0).
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