美国海关网站上有细则，
https://help.cbp.gov/app/answers/detail/a_id/619/kw/Canadian%20Citizens

Visiting the U.S. - Documents required for Canadian Citizens / Residents / Landed Immigrant to enter the U.S. and how long they can stay
What are the documents required by Canadian Citizens/Residents/Landed Immigrants to enter the U.S. and how long can they stay?

Canadian citizen's passports are NOT required to be valid for six months past their intended date of departure. Their passports must only be valid up until the date of their intended departure.

All Canadian Citizens entering the United States by AIR are required to present a valid passport, or a NEXUS card when departing from Canada. Please be advised that if arriving in the United States on a flight not pre-cleared by U.S. Customs and Border Protection (CBP) in Canada, Global entry kiosks cannot be used by passengers only holding a NEXUS card, and the regular inspection lanes have to be used.