I have been catfishing off & on for years but never seriously until I got bit by the cattin bug this fall when we were living in texas for a while. That said, I'm probably not the best one to ask about flatheads or blues. As far as the channel cats around here you just need to go to the grocery store & stock up on chicken liver. It's the best bait for channels I've ever found.
As to flatheads, I just emailed the DNR the other day & they told me that:
"Flathead catfish are typically found in large rivers in south west
Michigan. The lower Grand, Kalamazoo, and St. Joe all have flatheads. As
you move upstream in these systems, the type of habitat that the
flatheads like becomes more limiting and the rivers get smaller. We only find
flatheads in the lower 30 miles of these rivers."In your area the Grand River should be pretty good.