East on US 2 from Columbia Falls and south on US89 to Helena and US12 to Townsend to I-90 is 351 miles.
West side of Flathead Lake via 93 is 340 miles
East side of Flathead Lake via SR35 connecting to 93 south to I-90 just west of Missoula and then east to Bozeman is 323 miles
East side of Flathead Lake via SR83 along the Swan River to Condon and Seeley Lake to 200 to Ovando to SR141 to Avon to US12 to Garrison and I-90 east is 312 miles
Hard to say which way is most scenic - flip a coin. :) We've tried them all and they all have beauty to us.