If you go from Calgary to Vancouver via the trans-Canada highway (Don't take the Coquihalla Highway cutoff), you will have the opportunity to see lots, but it tends to be more touristy. The traffic can be a pain during the summertime, esp if you get behind slow moving trailers or RVs trying to negotiate the steeper parts of the highway.
Jasper to Vancouver via the Yellowhead is, in my opinion, the more scenic route.
I would agree with the first person who posted - take the Yellowhead going one way, and return via the TransCanada the other way.