Yes they will, because the event is possible. They want to be ready for unlikely possibilities through spending a couple of weeks to a day or less war gaming. Canada is not possible, other situations are possible. They are not likely, but they are possible, and are thus war gamed.
But I must APOLOGIZE to you. My link that I have been going on about you not addressing, went to blank. Since you, nor anybody else pointed it out to me, I had to just happen to notice it myself, by clicking on it.
article
The US has had multiple iterations of plans for invasions of countries that are currently (and were at the time) allies, as well as plans for defensive or offensive wars based on who our allies were at the time. If those aren't outlier scenarios then I don't know what is.
See Warplans:
- Rainbow 1 was a plan for a defensive war to protect the United States and the Western Hemisphere north of ten degrees [south] latitude. In such a war, the United States was assumed to be without major allies.
- Rainbow 2 was identical to Rainbow 1, except for assuming that the United States would be allied with France and the United Kingdom.
- Rainbow 3 was a repetition of the Orange plan, with the provision that the hemisphere defense would first be secured, as provided in Rainbow 1.
- Rainbow 4 was based on the same assumptions as Rainbow 1, but extended the American mission to include defense of the entire Western hemisphere.
- Rainbow 5, destined to be the basis for American strategy in World War II, assumed that the United States was allied with Britain and France and provided for offensive operations by American forces in Europe, Africa, or both.
War Plan Black
A plan for war with
Germany. The best-known version of Black was conceived as a contingency plan during World War I in case
France fell, and the Germans attempted to seize French possessions in the
Caribbean Sea, or launch an attack on the eastern seaboard.
War Plan Gray[13]
There were two War Plans named Gray. The first dealt with
Central America[13] and the
Caribbean, and the second dealt with invading the Portuguese
Azores.
[14]
War Plan Brown
[15]
Dealt with an uprising in the
Philippines.
War Plan Tan
[16]
Intervention in
Cuba.
War Plan Red[17]
Plan for the
United Kingdom, with variants from British dominions: Crimson (Canada), Ruby (India), Scarlet (Australia), Garnet (New Zealand), Emerald (Ireland).
War Plan Orange[18]
Plan for
Japan.
War Plan Red-Orange
[19]
Considered a
two-front war with the United States (Blue) opposing Japan (Orange) and the British Empire (Red) simultaneously. This analysis led to the understanding that the United States didn't have the resources to fight a two front war. As a result of this, during World War II it was decided that one front should prioritized for attack while the other was to be defensive, for the war in Europe against Germany and Italy and against Japan respectively. This decision resulted in the
Plan Dog memo.
War Plan Yellow
[20]
Dealt with war in
China—specifically, anticipating a repeat of the
Boxer Uprising (1899–1901).
[21] War Plan Yellow would deploy the US Army in coalition with other imperial forces to suppress indigenous discontent in the
Shanghai International Settlement and
Beijing Legation Quarter,
[22] with
chemical weapons if necessary.
[23]
War Plan Gold
[24]
Involved war with France, and/or France's
Caribbean colonies.
War Plan Green
[25]
Involved war with
Mexico or what was known as "Mexican Domestic Intervention" in order to defeat rebel forces and establish a pro-American government. War Plan Green was officially canceled in 1946.
War Plan Indigo
[26]
Involved an occupation of
Iceland. In 1941, while
Denmark was under
German occupation, the US actually did
occupy Iceland, relieving British units during the
Battle of the Atlantic.
War Plan Purple
[27]
Dealt with invading a
South American republic.
War Plan Violet
[28]
Covered
Latin America.
War Plan White
[29]
Dealt with a domestic uprising in the US, and later evolved to
Operation Garden Plot, the general US military plan for civil disturbances and peaceful protests. Parts of War Plan White were used to deal with the
Bonus Expeditionary Force in 1932.
Communist insurgents were considered the most likely threat by the authors of War Plan White.
War Plan Blue
[30]
Covered defensive plans and preparations that the United States should take in times of peace.
https://en.wikipedia.org/wiki/United_States_color-coded_war_plans