They wouldn't ban trucks carrying cargo, supplies, etc.
Every trucker who goes to Canada pops into a Tim Hortons before heading back to the US, no exceptions.
Disallowing close-packed passenger travel while still allowing essential logistics _curbs_ even if it does not halt. Just because it's not the solution doesn't mean it's not worth doing.
I'm saying that, epidemiologically speaking, Canada and the US should be treated as one entity. This is probably the case for border regions of Mexico as well, though I see no reason to allow flights to or from D.F. at the moment.
If (it's probably when) we start to see domestic travel restrictions, curbing transport between states, that's a good time to restrict the border as well.