This is getting a lot of play in Vermont, as it's expected to have a huge impact on business here. Effective February 1, you will not be able to cross the border from Canada to the US without proof of citizenship. The real wrinkle here is that US citizens will not be immediately required to present such proof to cross into Canada. If you cross without proof, getting home might be a problem.
The other problem here is, even if you have your passport, the mess at the border is going to be so extreme that the lines are going to be hideous and the border crossing guards are going to be in foul humour. Be prepared.