Here is one resource:

https://www.dnr.state.mn.us/state_pa...it/wheels.html

Portions of Adventure Cycling Association's Northern Tier route incorporate some trails in MN. You might want to get in touch with them.

An issue you might face is finding camping right along a trail. Might have to venture off trail a bit for that.

Not all unpaved trails have a hump in the middle. An unpaved trail with a nice, crushed limestone surface can be a joy to ride. You may have to compromise because there are just not that many long, paved trails. At 112 miles, the Paul Bunyan Trail (linked to above) is the longest continuously paved trail in the entire country.