Depending on time you have available, doing the ‘great loop’ can be fun that time of year. But that entails driving ‘around’ GNP (as the park really isn’t open)via East Glacier, St Mary, then up into AB via Waterton NP. In Pincher Creek you can go west to Fernie (and enjoy southern BC/the Kootenays), or up along the western spine to Radium, Golden, Revelstoke. Once in Revelstoke, you have a couple of directions to head back to Seattle. Regardless of ‘where, amazing scenery. With lots of snow but roads should be all clear. Radium Hot Springs, Banff Hot Springs are worthy. Skiing in Fernie is second to none, as is Kicking Horse, etc. The small towns in BC offer a lot once stopping and venturing.