Thanks Tee Jay, I am going to have lunch tomorrow with 2 friends and see if either wants to do the trip. I am open to leaving as late as May 8 or so. I've crossed at Sumas many times, but never went toward Kamloops from there. We just went through Hells Gate and followed the Fraser River - it's steep but gorgeous. But that was just in the truck.
The time we towed a trailer full of excessively heavy household goods we went via Montana, Calgary & Edmonton to avoid the hills, and the time we towed a jitney we went via Osoyoos to Princeton & Merritt on the advice of our Canadian friends. Thanks for the offer - I'll be in touch!