I'm not sure how you're planning on travelling in BC but I would highly recommend trying to, for example, start in Calgary, spend time in the Canadian Rockies, pick a scenic route across BC to the coast and enjoy mountainous country in the Kootenays, Okanagan or whatever along the way. (or opposite direction) Experiencing a taste of both the interior mtns. and the coast is a great intro trip to BC that is the way to go in my opinion.
Alternatively, you could rent a car out of Calgary for a week or so and see the interior mtns and then rent a car in Vancouver and Whistler and Vancouver Island (eg Tofino etc).
Coming to the coast via "the Duffey" (ie the northern portion of Hwy. 99 north of Whistler) and down through Whistler, is, as stated above, a nice option.
If you can jam it in as well time-wise, Tofino/Pacific Rim National Park is a great side trip.
Rented car or rented RV offer the best flexibility. My guess is that the RV rental places may be used to Calgary to Vancouver one way rentals but you'd have to check. May there's something on that in this forum.