Just returned from the trip. Used only ACA's Sect. 3 (middle) and 5 (very end) as it turned out. The fears of fracking boom truck traffic on Rt. 2 in the Williston, ND area are overblown now that the boom has passed. In fact the widest shoulders of the trip started at the MT/ND state line and stayed fairly wide from there past Minot. They alternated between wide and narrow the remainder of the way across N.D.
I had to make a decision in Wolf Point, MT about following the ACA route south for about 100 miles to Circle, Glendive, and Wibaux, MT and then east to cross ND to Fargo or stay on Rt. 2. With all the local advice being that there was no reason to fear the traffic on 2 and with a really strong west wind behind me I stayed on 2 and ended up with 100+ miles on the day. The wind strengthened the following day and I netted 120 miles. It was good to have those miles in the bank with a bus to catch in Duluth at a specific time and a train connection to make in St. Paul at the end of the bus ride.
The winds seem to be pretty much westerly when the weather is dominated by high pressure but when storms roll through the area they shift to more easterly. I fought heading crosswinds (but never total headwinds) for almost four days as I exited ND and entered MN. It wasn't until I reached the forested part of MN that I got some relief from them. The winds shifted back to westerly for the remainder of the trip across MN despite continued rainy weather.
Not sure if local opinions regarding traveling through the Fort Peck Indian Reservation in MT were at all an additional factor in ACA's route change. Without the strong tailwind I would not have been able to get through the reservation starting in Glasgow and ending in Culbertson all in a single day. I was warned repeatedly by both whites and at least one native not to let night fall while still on reservation land. I was especially warned to avoid stopping in Poplar. I'll admit to having some strange encounters while crossing reservation land though I never felt my safety was at issue. It was also a Saturday and that might have been an additional factor.
In terms of highlights I recommend the Paul Bunyan Trail section from Bemidji to Walker as worth taking if you have the time to swing up that way. Can't speak to the Heartland Alternate section as an equally pleasant but shorter route to Walker. If I'd stuck to my original plan I would have gone that way. As it turned out I was ready to get a break from the Hi-Line (Rt. 2) and it was a very pleasant contrast. Had to rejoin 2 to reach Duluth but a day off was welcome.
No guarantees this info will hold up for next cycling season but if someone searches "Norther Tier" in the next few months wondering about route conditions and reads this, you're more than welcome to p.m. me for more specifics.