This wouldn’t happen today. Today there is talk about Canada becoming 51st state; there is relatively little opposition to that - on the contrary, the perception of Canada as a US ally drops in the US[1]. Four more years of this and I could see people similarly accepting tanks. And if you want to prevent this, the time to act is now.
Surely no one currently in power wants Canadians to vote in U.S. Federal elections? So it has to be a setup like Puerto Rico (U.S. citizenship without representation in Washington) or even American Samoa (no U.S. citizenship). The 51st state thing does not make sense at all.
[1]: https://apnews.com/article/trump-poll-allies-enemies-friends...