I just assumed you wanted to go south.
I've been both ways & thought maybe you wanted to go through Jackson Hole, Yellowstone & then to Glacier National.
Hwy 95 & 12 are great, and a much prettier drive.
Heading North from Cascade & when you get to Grangeville, turn off 95 and go through town & take Hwy 13 east. It will take you to Kooskia & connect back to Hwy 12. That will cut considerable miles off the trip.