"Non-discretionary" travel through Canada to Alaska by the most direct route is permitted. I don't know how rigid they are on non-discretionary. It includes Alaskan residents returning home, business travel, etc. but other than that may be at the whim of the border agents. As Glasseye mentioned there have been some cheaters. Besides what he referred to I've heard of US residents at resort hotels. If you are thinking of giving it a try, I'd phone the CBSA office at the planned border crossing and see how they are applying the rules. You should also be aware that Yukon Territory has a limit of 24 hours to pass through their real estate on the way to or from Alaska. The US-Canada border closure applies both ways, btw, by mutual agreement. Canadians are restricted from ground travel into the US. Our Covid situation isn't by and large as bad as in the US, but the case numbers are growing again since the bars opened.