Taking the average attendance at Michigan's last ten bowl appearances (74,735), I then made an assumption that approximately half of those were Michigan fans historically (37,367). Allowing for the relative attractiveness of this matchup, add a potential 5%. So, I would go with something in the 37,000-42,000 range.
Hockey pet peeve: "when a teammate tips a puck in on you, which is exactly how my first collegiate goal against happened. Thanks, Copper."