If US and Britain has fought on opposite sides during WW2 or any equivalent scenario, will Canada stick with British Empire or will it jump immediately to US camp ?
I'm only aware of plans made post-World War One, so most of this is based on 1920s-early 1930s information.
"Defense Scheme #1" was the Canadian plan, which called for simultaneous
all-out assaults on several cities near the Canadian border (such as Seattle and Albany) at the opening of hostilities. Obviously this was not meant to be a glorious blaze of conquest, but rather to distract as many US forces as possible from invading Canada itself, thereby lessening the effectiveness of the US assault and buying time for assistance from the UK to arrive. When the Canadian forces encountered "significant resistance", the plan was then to swiftly retreat back to Canada, employing scorched earth tactics along the way.
Official British plans are more vague - specifically, they did not exist, as the British government disallowed planning exercises against the United States in order to discourage the Royal Navy from justifying a naval arms race against a nation they viewed as a natural ally. While it would be nice to think Britain would support her dominion(s) to the best of her ability, it was generally accepted that
Canada would be effectively abandoned as the British knew the prospect of a large-scale invasion or even just blockading the United States was considered unrealistic at best. It would be a naval war, with the primary objectives of the Royal Navy being to harass American trade and raid the American coast while defending British trade, and above all else to defend the British Isles which were considered devastatingly vulnerable to blockade. By
forcing a stalemate, a negotiated settlement would eventually be reached.
The American strategy,
"War Plan Red", is as simple as it is ruthless. The primary objective would naturally be to prevent Britain from assisting Canada. Halifax, as a major city and Canada's largest port, would be the primary target, to be secured following a
poison gas strike (!) on the city. Securing Quebec City, Montreal and Toronto would capture Canada's major population centers as well as the Great Lakes. This, along with the capture of Winnipeg, would effective cut the country in half and secure Canada's rail system. Vancouver and Victoria would be secured to deny Canada access to the Pacific and greatly hinder British forces in the Pacific from participating in the war directly.
Having secured and isolated Canada from the Empire, US strategy was to simply
wait. The US Navy would secure the North American coast and wait for favorable opportunities to engage smaller British fleets. If successful, the advantage would be pressed and British shipping and colonies in the North Atlantic would be targeted. Notably, although the American plans were quite conservative and
defense-oriented, British naval planners did not expect to be able to resist a major US Navy attempt to directly blockade the British Isles, which would obviously bring the war and the "stalemate" strategy considerably in the United States' favor.
At the war's conclusion, it was intended that captured British territory (specifically and primarily Canada, though any captured Caribbean/Central American territory would likely also come into play) be
annexed: "The policy will be to prepare the provinces and territories of
CRIMSON [
Canada] and
RED [The
British Empire] to become states and territories of the
BLUE union upon the declaration of peace."
In the event that Canada declared its
neutrality in a United States - British Empire conflict, the plan advised that Canada's neutrality be accepted only on the condition that the US be allowed to effectively take over Canadian ports and strategic locations for the duration.
TL;DR version:
Assuming a one-on-one scenario, parts of Canada and probably quite a bit more are going to be joining the United States.
