Very, very flat and scenic...28-June Menononee River Century. It is a little north of Green Bay. Nicely run, considered worth driving for.
Other than that, I'm located south so I'm not familiar....but you might want to keep an eye on the events calendar at the wisconsin bike fed (bfw.org). If you race, there are now two multi-stage race series, one before and one after the 5-july. The bike fed site references them both.
Or, grab a route sheet for the Door County Century and do a self-cater. Nice route.