Going to the sun road is a must see, but I am sure you have already planned that, start off early to beat traffic, before 9 am, or later evening when everyone is having supper. nothing like being stuck behind a van. The past few years there has been a lot of construction on the pass, should almost be done this year.
From East Glacier you can take 49 to 89 to St Mary's, stop by the Park Café in St Mary's for Pie than up over the pass.
Depending on What your riding, Kintla Lake or Bowman Lake are nice out of the way camping, but a lot of gravel. Camping usually fills up early, especially on the weekends.
Feel free to contact me if I can help out on this end, I am from Alberta but spend most of my summers weekends down in GNP. I know I will get some slack over this, being Canadian, but Waterton Park is a nice place but more pricey and more commercial, Nice to see but not a must see.