It's ridiculous to consider Canada or Mexico (or if we extend this farther, the EU and Japan) "vassal states". All of these countries participate in the US Capitalist regime willingly because they get rich too.

By your standard, do any of the considered "major alternative powers" (China or Russia) have allies?

Very accurate. The CIA is actively involved in the interference of their 'allies' governments.

Japan didn't break from US in this news article, it received permission to do so, likely so that it can remain in a defensible position against China.

Canada and Mexico aren't vassal states.