Canada West was Canada, it did not have to join. It was part of the United Province of Canada. Western Canada was purchased by Canada, it, the inhabitants, had no say in joining. Even less after Canadian troops were sent in to make the pro's very clear.
There is no King of Canada. Canada retains ties with the Commonwealth and recognises Queen Elizabeth II as Queen of Canada, although she has no powers or any say in the daily business of Canada. Her role is strictly ceremonial.