I think one of the most scenic drives anywhere is Alberta's Cowboy Trail (highway 22). This is about a 200 km stretch of road that extends southwest from Calgary, along the region where the great Plains meet the Rocky Mountains. It's where cowboys used to guide huge herds of cattle between Montana and Alberta before fences were put up — and is how the road derived its name.
A few weeks back my wife and I drove from our home in Idaho to Calgary to catch a flight to Winnipeg for one final visit with my father. The day was clear, if cold, and the views were lovely. I've never grown tired of the scenery here.
You're guaranteed to see ranches and farms, and large herds of cattle on your trip. Frequently you'll also see wildlife including elk, moose and deer. One of my sons spotted a pack of wolves beside the road during one of his trips, although I've never been that lucky.