Thanks to everyone for the suggestions, here's the draft plan for our trip next year, probably about the 3rd week in September:

Day 1 - Drive from Baltimore MD to Columbus OH, stay with friends.
Day 2 - Drive from CMH to Glen Arbor area
Day 3 - Biking Leelanau area - Leelanau Trail
Day 4 - Biking Leelanau area, Sleeping Bear Heritage trail area, maybe drive/ferry to Mackinac that day
Day 5 - Mackinac Island Day with bikes.
Day 6 - Ferry/drive to UP, do something somewhere UP
Day 7 - Long Drive home or Drive 1/2 way back, stay somewhere. Could do some GAP cycling if want to extend near PGH.
Day 8 - Remaining drive day

From the suggestions, we zeroed in on the Leelanau peninsula for the biking days. Mackinan Island is on my wife's bucket list. The short amount of time in the UP will probably be a hiking or rent a kayak day.

Any critiques or suggestions appreciated.