Quite a few years ago, I flew from the Ely float plane base to the Beaverhouse ranger station.  Enroute, we landed at the Sand Point custom station, where passports were checked (this is pre-card days).  I'm reasonably certain that Sand Point would accept a passport card since a majority of their traffic is from tow boat traffic headed from either Anderson's or Zup's for entry at via LLC to the southwestern part of Quetico.

But the short answer would likely be to check with your flying service. They would almost certainly know the answer.

dd