The upper St. Louis is your best bet
The upper St. Louis is your best bet(class II-III) Pretty much all of the other north shore runs are creeks(class IV-V+) that are way too technical for rafts, although there may be an exception or two with high water. Not too sure about the southern stuff as I spend most of my time on the North Shore. You may also want to look at the Montreal in the U.P. of Michigan which is a fun playboat run anyways. The Vermillion near crane lake in northern minnesota near canada may be okay to raft as well with enough water, although the whitewater sections are somewhat short, but it is more of a wilderness run and the fishing would be good at camp.