I like the visual of this thing hanging in the sky among the stars.
I find it odd that the US would see the need to nuke Canada, as conventional forces would have a pretty easy time of it, and unless the nukes were tiny, they would be obliterating a good portion of their own population. Detroit, New York state, Oregon, etc. Most of our population is within 100 miles of the states and it would seem like using nukes in a civil war. That and I expect by the timeframe in question, a huge amount of the american water supply would come from Canada.
A military organization, the Stalkers are a hunting/mining militia that are known for wearing full body shrouds that easily hide them in snow and other slushy terrain. The lightly armored warriors are known for the speed, stealth, and the vicious wounds inflicted by their hunting hatchets. Many of the Stalkers keep crop-eared warhounds with them, both for hunting, companionship, and in war.