While US celebrates its independence, Hawaiians still wait for theirs
sfgate.com
sfgate.com
I'm actually not sure? Prima facie, I think it would in fact be legal for Congress to conquer and annex Canada. A bad idea. But the constitution does not seem to prohibit it.
Anyway, while the premise of this article is cute, it forgets something about the right to self-determination. It includes the right to choose "incorrectly". In practice, as things currently stand, if you gave the population of Hawaii the vote on this, they'd vote to join the United States. So speaking of an independent nation of Hawaii, as if it would ever exist is essentially fantasy.
Here in Canada, provinces have a clear legal right of secession from federation; they're sovereign and they may exercise that sovereignty. The biggest reason none have actually done so, I think, is that it would simply be a massive headache for little clear purpose.
It would be legal within the US where the governing law is the constitution. It would not be legal outside if the US. Which is the point the original article was making.