In many disputes regarding boundaries between the US and Canada, the British were more than willing to go overboard in negotiating and coming to an amicable accommodation, often to the detriment of the Canadians. The British often were less than accommodating when it came to other disputes around the world. So, at what point is it likely that if an actual war is started by the Canadians would the British just wipe their hands clean put them up and say "you're on your own" as long as the Americans made it clear they aren't attacking anything else. Included in the definition of "Canada" is anything currently Canadian regardless of when they joined (such as British Columbia, Newfoundland, at any time period).