If Canada were to allow China to start building military bases and anti-ICBM defense sites on the Canada/US border, there'd be regime change on Parliament Hill within the week.
Every empire needs aligned, friendly, or at least, neutral buffer states on their borders - and will violently defend incursions into their buffer zones. Observe the shitshow over Cuba - sixty years of sanctions, terrorism, assassination attempts, an invasion, and a nuclear crisis later, the United States still hasn't forgiven it.
The United States was ready to bathe the entire world in nuclear fire - because a neighbouring country entered into a military alliance with the USSR. Let that sink in... And then consider what expanding NATO into Eastern Europe, US support of Georgia, regime change in Syria looks like from the Russian point of view.
At the time, Turkey (Which shared a border with the USSR) had US missile bases, full of nuclear missiles pointed at Moscow. [0] When the situation was equalized, the US lost its mind.
Meanwhile, in the present, 21st century, the US is busy building a missile defense shield in Poland. [1] (While claiming that it is built to defend against, of all places, Iran. [2] Seriously?) It is intended to neuter Russian nuclear capability... Meanwhile, Minutemen ICBMs continue to be able to strike Russia.
I ask again - how would the US react if China, or Russia started building army bases, and anti-ICBM installations in Canada, Mexico, and Cuba? How would the American empire respond to a political incursion into its buffer states?
That's what you're replying to. Several former Warsaw Pact countries joined NATO. The West didn't invade them.