Recommended route from Portland, OR to Glacier NP?

I agree with those who recommend camping on both sides. We did that last summer and were very glad we did. In our case, we spent 5 nights on the west side and 4 on the east, but almost any combination of at least 3 nights each side would work well. Otherwise you'll just find yourself driving a lot many of the days you're there just to get to the places you want to hike or photograph.

US 2 between east & west sides is no issue whatsoever.