From Calgary as well and did the same trip for 3 weeks in September last fall. We did similar going to Spokane and then did the coast the next day. It is a long run on the second day and if we did it again would probably split that day up and maybe go to Portland or so and then hit the coast the next day. Most people have mentioned places we stayed along the way and they are all nice parks. I am not sure about that time of the year but even in September you could hardly get a camp spot without a reservation so keep that in mind too or you may have a challenge stopping at a decent spot. If you need any info feel free to pm me and I will be glad to answer anything especially from this area out. We had our TT and the in laws with their fifth and was a great trip. 3 weeks was almost not enough and wished we had another week or 10 days as we had stops we would have liked to spend some more time.