If you want to have a two or three month adventure, I wouldn't try to visit much here in the U.S. Instead, I'd explore Canada on the way to Alaska.
You might consider taking the Trans Canada highway 1 across to Calgary and see the various Provinces along the way. The downside of this route is that gasoline prices are higher north of the border. The alternative would be to work your way west on I-90 and then head north at Missoula. You could spend a few days exploring Glacier NP (US version) before heading north to BC 93 through Kootenay National Park to Banff. You can easily spend a week or 10 days just exploring Banff, Yoho and Kootenay from a base camp at Banff. Then head north on the Icefields Parkway up to Jasper. Again, one can easily spend another week in this park.
These parks along the Alberta/BC border are some of the most scenic mountains we have even seen. I've been in Alaska for 3-4 weeks a couple of times, and for me, the Canadian Rockies in many ways are more beautiful. (Of course Denali is in a whole league by itself.)
