Fall or spring is not the right time to be in northern Montana or Alberta, especially if you are from the South. A lot places will be closed and you may encounter snow at any time. Fall is better than spring because at least the roads will have a better chance of being open.
I remember living in Colorado in the 1980s. I planned a Memorial Day trip to Grand Lake which is the largest natural lake in the state at around 6,800 feet. I came over a rise and was amazed to see that it was still frozen solid.