My son and I did that trip two weeks ago. About 65 miles. Are you going to get off the bike trail in Barre Mills and then retrace back or just stay on the bike trail past the turn off?
Also on Monday I rode north out of Bangor and that trail takes you down by the Black River just on the outside of town, WET,WET,WET. The Black must have backed up and flooded that area. We made it but be careful. I'm not sure if there is another way around, none that I know of, maybe Paul K. will read this and can comment. Lots of blacktop through Onalaska, not cool. The ride from Mindoro to Burn has some of the coolest trails, Olson's Cultch is as steep and narrow as you would want, beautiful. Sounds like a good time.
Another nice trip is north on the Bike Trail to Trempealeau then Galesville to Etrick over to North Bend and back to Holmen, thats around 75 miles. North Bend as a couple local bars with grills. You can't go wrong on any of these trail. Remember Onalaska trail closes at 10 or 10:30p.m.