1. Some people freak out in summer when trying to drive the Alaska Highway. It is a tough trip.
2. The border is closed to some, not to others. I can fly out of Toronto to many US destinations, no problem. I have two children who live in Canada and work in the US. They cross the border every day.
3. My wife has a US passport and a PR card for Canada. She cannot be denied entry if she presents herself at the US border because she is a US citizen. She cannot be denied entry if she presents herself at the Canadian border because she has permanent resident status in Canada. Border services might ask her a lot of questions, they might require her to quarantine, but they cannot deny her entry.
It is a "soft" border closing.
Have you read about the people in Pt. Robert’s being stranded and not being allowed into Canada to transit to the main part of the US? Look at the map of rather border just west of Blaine, Washington. There is this weird little bit of land jutting down below the 49th parallel which is U.S. land and isolated from the rest of the U.S.