Have you already "done" the Northern California/ Oregon coast? If so and you'd like to see National Parks, I'd recommend taking I-5 up into BC, BC-1 (a.k.a. Trans-Canada Hwy) over to Kamloops and through Glacier and Yoho National Parks and into Banff. While the chateau at Lac Louise is very nice, we stayed at more affordable and bigger rooms in Canmore.

From Banff back to San Francisco you may want to try heading east to Calgary and then down south along AB-2, 3 and 4 until you get back into the US of A and heading down I-15. That will take you all the way down to US-89, and that will take you through Yellowstone and Glacier National Parks. To get back to I-15 take WY-22 west to ID-33 west to ID-31 west to US-26 west (it sounds a lot harder than it is). At Pocatello take I-86/US-30/I-84 west. Around Twin Falls US-93 south will take you down to I-80 west and your path home.

Once you decide on the general route you can work on the specific things to see. My recommendation is based on trying to fit in as many beautiful national parks in a reasonable time (e.g. not taking dog-legs to Glacier or North Cascades National Parks that may end up adding too much driving).