The group’s problem appears to be that there is very nearly zero desire for such a union in either country.
I wouldn’t personally be averse to some of the Canadian provinces joining, if their people desired to, but I’m not interested enough to spend time promoting the idea.
The Canadians in many ways have the best of both worlds. They are protected against any potential threat by the US military, which they don’t have to pay for, and they can spend their time lecturing us about the evils of our militarism.