The military of every country is, or should be, working on plans for invading their neighbors. I say "should be" because you never know when the winds will suddenly blow sour and cause you to wish you already had those plans drawn up. In addition to Plan Red, we had War Plan Orange, which outlined the conquest of Pacific islands formerly owned by Germany, that had been given to Japan at the end of WWI. Parts of that plan were used by the USMC in WWII.
If ISIS established a toe-hold in Canada, wouldn't the public expect the U.S. military to be able to invade for self-defense purposes?