I try to avoid US 2 in most places west of Glacier NP.
Especially west of Kalispell, it is narrow with limited shoulders.
Plus it has moderate-plus traffic including logging trucks and big RVs.
I don't know what it is about Montana -
Wyoming generally has good shoulders, Montana doesn't.
They are working on it all over the state - including US 2.
But veeerrrrryyyy slowly.
Here's a rough scale of cycling comfort:
+3 - Pure Heaven
+2 - Sweet
+1 - Nice
0 - Meh
-1 - Irritating
-2 - Uncomfortable
-3 - Pure Hell
I'd give that stretch of US 2 a -1.5.
And it all depeds on when you hit it.
Summer traffic is much higher than winter traffic.
With Kalispell's growth - there is a morning/evening commute pattern.
Friday afternoon/evening tends to have heavy outbound.
Inbound even more concentrated Sundaly late afternoon/evening.
There is a fantastic PAVED forest road from Trego to near Libby.
The road has so little traaffic that I changed my shorts in the middle of the road.
And I took my time.
Don't know where you are coming from east of Kalsipell.
And whether or not Kalispell is a "must".
Whitefish is really nice and not as big.
Even so, you have a short stretch of narrow US 93 on this option.
(Road thru Kalispell this past summer - pretty intense for miles in all directions.)
Link to journal entry for Trego Road -
https://www.crazyguyonabike.com/doc/page/?o=1mr&page_id=62782&v=5w