There is both a fan created Cascadia Cup which while not endorsed by the league is a real thing. The teams and fans care about it. 

https://cascadiacup.soccer

And yes there is a regionalist movement which some people advocate for independence from Canada and the US. It’s got a flag and adherents. The polling for it is surprisingly strong, between 30% and 50% as a theoretical question, but there is no actual real proposal. If it came down to it who knows what the vote would be. That said nobody thought brexit would pass. I don’t think Cascadian independence is likely or a serious movement the way Scottish or Catalan independence movements are. Plus the region would have a lot of the same political polarization that exists in the US, except the power would be more strongly held in the cities which would cause resentment and opposition from rural conservatives. So meh. It’s exceedingly unlikely anything would happen. 

https://en.m.wikipedia.org/wiki/Cascadia_movement