Highway 2...west to east

I rather enjoyed the Havre Beneath the Streets tour (in Havre, MT). The buffalo jump in Havre is supposed to be one of the very best preserved ones, too, and well-presented, but I haven't seen it personally.

If you don't mind dry camping, the Nelson State Recreation Area between Malta and Saco, MT is pleasant (on a lake) and free of charge.

Be sure to plan one stop in far eastern Montana at Fort Peck Corp of Engineer park. It is interesting and has large grassy sites... makes for a nice break.

For a 2 night stop consider going to the Peace Gardens 12 miles n on US 281 n. of Dunsieth ND. They straddle the US CA border, are uniquely situated in a prairie montain highland. The area within the Peace Gardens in a no mans land, so no border crossing inspection into the other country is required, only reentry into the country of origin.

Speaking of small towns, Glasgow, Mt on US2 is the 'middle of nowhere':

Wiki quoting a recent WP article wrote:
Using data from Oxford University's Big Data Institute, The Washington Post, in 2018, identified Glasgow as "the middle of nowhere" for the contiguous United States. The articles stated "of all towns with more than 1,000 residents, Glasgow...is farthest — about 4.5 hours in any direction — from any metropolitan area of more than 75,000 people."

That's true of most of US2. I suspect Duluth is the next biggest city on US2 after Spokane. Kalispell Mt and Grand Forks ND are probably the distant runers-up.

If you’re a railroad buff in the slightest, it’s a great destination. US2 is also known as the Hi-Line and basically follows the railroad. Lots of history.

We've had more fun simply asking the locals "what's to do here" there are many very nice campgrounds along the way.