If you're looking for the fastest route, I generally take US 93 south from Kalispell to Elmo where I turn rt onto MT 28. At MT 200, I turn left for a few miles to MT 135 (really pretty drive along the Clark Fork River) to St Regis where you'd turn rt onto I-90 which will take you over Lookout and 4th of July Passes. As an alternative, you could turn right at MT 200 and head to Sandpoint ID (this would be farther, but this route is very scenic). Depends on whether you're trying to make good time or enjoy the journey.