As far as the US government is concerned, No, with a valid green card, you do not need a passport to enter the US, no matter how you travel. From this FAQ from the CBP:U.S. LPRs do not need a passport to enter the United States as per 8 CFR 211.1(a), [u2026]Or see the CBPu2019s Carrier Information Guide (page 28):A Lawful Permanent Resident may travel to the United States without a passport with a Permanent Resident Card (Form I-551).It is possible the airline may require you to have a passport even though the US doesnu2019t require you to. However most flights from Canada to the US go through US preclearance in Canada, in which case the airline would not have any reason to care about travel documents anyway, as you would have already u201centeredu201d the US prior to the flight (which is basically considered a domestic flight).