It would seem to me that you will need to decide what works best for you to access I90 and how far you can go the first day taking in to consideration ferries off of Vancouver Island. One could travel hwy #3 Hope to Osoyoos and go south to Bridgeport and travel to hwy #2. Or go south of Seattle and catch I-90. We always enjoy Grand Coulee and try to catch the laser show that is projected onto the spillway of the dam. We enjoy Springbank or Spring Brook campground on Lake Rooseveltpart of the recreational area on Lake roosevelt. Then travelling #2 you can meet up with i-90 in Spokane and then travel onto Bozeman. I have enjoyed #191west of Bozeman to West yellowstone, tour Yellowstone and then go north on #89 to Livingston. I have not been to Glacier National Park but one could vist there, acess Waterton lakes on the Alberta side and then proceed west on hwy #3 catching the communities you are interested in in B,c. interior. Kokanee Creek provincial park just north of Nelson is a great favorite and very busy espcially in the summer. If you have specific requests about the interior of B.c and provincial parks I can offer opinions.