If this is true and Canada has not arrested O’Leary then they’ve already shown how weak they are to naked sedition and it’s only a matter of time before something terrible happens.
Naked sedition would be promoting an actual invasion, not just floating the idea of Canada joining as the 51st state voluntarily and figuring out the logistics of how that could happen (which as far as I can tell is all this is).
We don't have an equivalent of the American Logan Act that would make this illegal.