I found out some info about the cruise ship plying the Great Lakes (or at least one of them. I don't know if there are more.)
The name of the ship is the C. Columbus. It ran a limited two cruise schedule in '98 with a full schedule to be run starting in '99. The ship itself accomodates 420 passengers, so probably not real feasible, at least with this ship, for a reunion cruise of the Great Lakes.
I'm still searching for more info though.
-Todd