Southern BC is mountains all the way across. The highways do their best to take the easiest route, but still some grades are necessary. From Banff there the 2 main options:
Hwy 1 (TransCanada) all the way. Climbs gradually to the provincial line north of Lake Louise, drops through Yoho to Golden, climbs again to Rogers Pass in Glacier NP (the Canadian one), back down to Revelstoke. From there it is river level all the way to Vancouver. However most traffic (especially if they are in a hurry) take Hwy 5 over the hill south of Kamloops. While has grades it is divided highway (once toll).
Hwy 93 through Kootenary NP is another way into BC. Then you can take Hwy 3 all the way across the south edge of the province. This has several passes. But it also has beautiful variations like the drive north on Kootenay Lake and the ferry over to Nelson.
There is a 3rd option - 93 north through Banff to Jasper NP. Then Hwy 5 SW to Kamloops.
I like to use BC provincial parks. They don't usually have hookups, but they have large, well spaced campsites, and many have good hiking.
There's no shortage of tourist information at provincial visitor centers. Also books and map books at groceries, bookstores, and even online. Look up Banff Nat Park, and download the newspaper describing that whole cluster of Alberta/BC National Parks.
DriveBC is the provincial road conditions website.
Google maps have terrain maps and streetviews for the major highways.