Definitely a paddle/pedal trip opportunity from Franklin Square to Lisbon with “shuttle” via the Greenway Trail. Above Franklin Square to Route 14 there would be several low water bridges to contend with, although the bike trail separates from the middle fork around Leetonia.
Canoeing Guide to Western Pennsylvania and Northern West Virginia (1991 edition and 2005
online edition) covers LBC including the middle fork. It says gage should be over 4.3 feet for this section. Based on my one-time experience, I think 4.3 would be too low, though as Ken points out, the gage is quite a distance downstream.