No firsthand knowledge of the WCBL, but next time I talk to my son I'll ask him. I would bet that he knows a few kids playing there. There are all sorts of US players playing up there normally. It's a pretty seamless transition playing up there normally, and the prairies and Rockies are beautiful in the summer, but Covid has changed everything. Who knows what it will be like in the spring, but as of now the Canadians have stricter quarantines than most of the USA, even though their death and infection rates are at a significantly lower level.
I would imagine that the teams themselves would have the best idea of what is going on, and would have a very hard time filling out a roster without American players. The covid situation is so fluid it's hard to say anything definite as of now...in three months everything could be well under control- or not.