Very cool, if true

If that was an open border, there wouldn't be a US customs "preclearance" area in the Montreal airport, with a separate post-customs concourse in the security area. Nor would I have to get off the bus and talk to immigration/customs people when I cross the Vermont-Quebec border that way.

Even back in the last century, there was usually at least a brief "what's your citizenship?" question at the border, though they might not ask for paperwork if you were in a private car rather than on a train or bus. (That's for roads between towns, rather than the sort of cross-border town calimac mentions.)