Hi Marge,
That trip was nearly 8 years ago. I feel that was one of a few trips where we could have left our tow vehicle home. BUT I feel a PC longer than a 2350 may benefit from a tow vehicle. You have a 2350 Sprinter so no worries that I can think of.
Traveling late summer early fall is going to get cold at night. July/August will be your warmest time. But even then, it can snow. Also keep in-mind that later in the year means shorter days.
There are 4 large provincial parks (Canadian National Parks) lumped together, Banff, Jasper, Yoho, and Kootenay. A day hike to Twin Falls in Yoho is so beautiful with a tea house to eat and enjoy the view from. That is one example of the "other" places not to brush off.
I do not have any documentation nor pictures posted any longer. We live near Chicago and our 3 week trip back then was too fast pace. You are in California. I recommend 4 weeks to slow down a bit and enjoy the trip at a more leisurely pace.
Ron Dittmer