The average channel cats tend to run larger in the mississippi. There are definitely flathead catfish also, although I only fished a few times on the mississippi (boat) for channels.
Maybe find some local bait shops and ask questions.
Will you be using a boat ? If so, it would be easier to move around and fish. I would try near shoreline cover just off the main channel, around wing dams, drop offs and holes in sloughs that have current, rip rap areas (maybe try float fishing cut shiners/minnows/suckers around the rip-rap.)
If you were bank fishing, find areas where the current swings close to shore, and look for rip-rap, cover, tributaries, etc)