I'm not the first author to write about conflict Canada between and the United States. I'll write today about two of my favorite novels in this genere. The first is Exxoneration, by Richard Rhomer (1974: Paperjacks).
The novel is the sequel to Ultimatum (1974: Paperjacks) which details a 1980 showdown between Canada and US over oil. Ultimatum ends with the President of the United States ("a Texan facing re-election"), announcing the fait-accompli annexation of Canada by the United States. In a maneuver worthy of Defense Scheme One, with waves of of US occupation troops on their way to land at major Canadian airports, the outgunned Canadian army is able to trap the US forces on the ground as they land, thus saving the day and forcing a US withdrawl.
The author, Richard Rhomer is no slouch: a decorated RCAF fighter pilot, he is credited with piloting the reconnaissance plane over Normandy in July, 1944 that directed the airstrke that killed none other than the Desert Fox, Erwin Rommel, who is a major character in War Plan Crimson.
The second novel, Bruce Powe's Killing Ground: the Canadian Civil War (1968: Peter Martin Associates), was written at a time (pre-October Crisis) when English Canadian and French Canadian tensions were just beginning to boil and no-one knew which direction things would take. Fortunately, in reality, cooler heads prevailed on both the federalist and sovereigntist sides and the violence never largely happened.
The book ends with the concerned United States government, under the guise of UN intervention, launching an invasion of Canada. How realistic is this particular scenario? During the previously mentioned October Crisis, which placed parts of Ontario and most of Quebec effectively under martial law due to two high-profile kidnappings by the FLQ, in October 1970, a former professor of mine at the University of Otttawa took a roadtrip to Morrisburg, Ontario, which is on the Canada/US border. He said he could clearly see American armor and other mechanized equipment lined up on the other side, ready to go. Although I can not confirm or deny this, I am still inclined to believe him.
Fortunately, neither scenario has come to pass and have remained just some very interesting fiction. In the meantime, you can always read another interesting fiction, War Plan Crimson, A Novel of Alternate History, by Michael Cnudde ($2.99 to buy as an e-book; free to sample).