Would you go to L.A. or NYC without prearranged plans for lodging?
You may have to stick to a fixed schedule.
You probably should plan for fewer daily miles.
But, then again, fewer miles means more time to enjoy the parks.
I've stayed at Red Earth, Hector Lake, Big Bend (x2), Kinney Lake (x2)
I've ridden the Spray River Trail - scouted out other bikeable trails.
I've also backcountry camped in Kootenay, Yoho, Kananaskis, and Elk Lakes.
You will be coming theu Prince George, BC. That's 2 1/2 days out of Mount Robson.
Use some time in P.G. to make online reservations - knowing what the weather looks like.
Remember that July 1 is Canada Day.