If you are riding to Montana on I90, another beautiful ride would be to exit I90 approximately 20 miles east of Missoula, MT and take Hiway 200 for approximately 22 miles to Hiway 83. Follow Hiway 83 north through the Seeley Lake, Swan Lake, and Condon areas. Hiway 83 terminates at Bigfork, MT; you are about 20 miles from Whitefish at this point.
1) This ride would be my first choice. I spent a lot of time thru there areas as a kid & loved the exposure I got from this much raw Mother Nature. Seeley Lake & Swan Lake are both relatively untouched. There are also a couple of working/Dude ranches in this area, if you're interested.
Be aware - Seeley & Swan Lake are adjascent to the Bob Marshal Wilderness. There have been instances where certain large furry four legged critters have exited the Wilderness and have attempted to make themselve at home in the public campgrounds.
2) would also take the Lolo Pass up to Lolo (almost to Idaho). There's a reall nice hot springs there at the top of Lolo pass. Operated by a Mom & Pop, with clean dressing rooms, clean towels. I stop here whenever I get the chance!
3) And as has been suggested, complete circle of FlatHead Lake would be in order. Stop at Yellow Bay for a swim!
4) When you're in Glacier Park, make sure you get over the the Many Glacier section. To get there you may have to exit out thru St. Mary's Lake and return at the Many Glacier Gate. Well worth it!
I'm seriuosly considering doing this rout in August, hopefully, if the fires aren't too bad by then.