Montana Club is not too bad. There is also a place (don't remember the name) right next to it that has pretty good BBQ.
If you have your WA CPL its honored in ID and MT so no major concern. Parks are left out of preemption unlike WA so you will need to look up the local code (seems a lot of them restrict it). MT is not a stop-identify state.
A note: You are required to open carry in any building which dispenses, services and allows consumption of alcohol. To be safe, I normally open carry at any restaurant that serves any alcohol such Montana Club.
I have never had an issue with OC in MT (used to live there).