Your post sounds more geared to off road routes and I don't live in the area but thought I'd chime in on my experiences in the area a number of years ago.
I took Amtrak out to catch a tour in West Glacier but due to problems with the Whitefish station I had to get off at East Glacier and bike across the divide. I took Hwy 2 and it was a very nice ride and I was surprised when I reached the top of the divide because it wasn't as difficult as expected. The route down through Essex and into W Glacier was wonderful.
As a group we biked back east across Going to the Sun Highway which was gorgeous. Don't miss out on this one! I think the west side is more scenic but you need to get an early start since they want bike traffic off the road by late morning.
Good luck!