Might contact the locals...
<http://friendsofcdatrails.org/CdA_Trail/#.Udn9hm2U_SM>
<http://friendsofcdatrails.org/Milwaukee/index.html#.Udn-um2U_SM>
The Route of the Hiawatha and The Old Milwaukee Road were/are gravel forest roads. Not bad on a FS mountain bike, but I had fat tires. Your bike would be happy on the Trail of the Coeur d'Alenes with camping at Heyburn SP, Harrison (at the marina) and in the Silver Valley at various locations. Probably less so on the gravel Forest Service roads.