Kind'a depends on how much high remote wilderness you wanna' fly over.
If you're going IFR you gotta' cross the continental divide somewhere and that usually means MEAs of 13,000 to 14,000 feet. The airway between Great Falls and Kalispell crosses quite a lot of high remote wilderness, beautiful country but if you go down the grizzly bears will prob'ly have you for lunch before you're found. I've made the crossing many times IFR and VFR between Cut Bank and Kalispell, up over Marias Pass (that's the route of the old Great Northern Railroad, lowest pass in the northern rockies, eight thousand will clear the next ridge west of the pass and from there it's all downhill into the Flathead valley. Prob'ly the most civilized (and lowest route VFR) would be head southwest out'a Great Falls right over the big square butte and up over Rogers Pass, thence over Lincoln and down the valley into Missoula, from there pretty much straight north up to Kalispell. That route's a little out of your way but it'd keep some semblance of civilization under you MOST of the way.
John C. Saubak
Peerless, Montana