The Cheboygan is a little tougher than the Black with generally deeper water, less weeds, and more boat traffic. If you can go up the Black from the confulence you will have little better experience. And the fishing will be pretty decent too with good numbers of pike, and the occasional musky.

Esox, i just got home from up there. The Cheboygan is very clear upstream from the Black. I would concentrate on the Black. The bays upstream have very good cabbage in them, and a lot of big pike, muskie and walleye like to hang out there.
To say the Cheboygan has a lot of boat traffic is putting it mildly. All of the Cheboygan however is no wake. Just upstream from the where the mouth of the Black dumps into the Cheboygan is an area called stump junction. Pull up your big motor and put your trolling motor to work.
In the evenings you can find a lot of pike and muskie in those logs.(even though I failed last week!)
Good luck.