Realistically WI is great for biking just about anywhere. We have it all - flat, hilly, urban, rural, coast, interior, farm ,forest.
I myself would either do the "Northwoods" maybe Vilas Cty, plenty of lodging, food etc.
http://www.northwoodsbiking.com/vilas.htm
And you can't beat Door county for scenery, good food, B&B's. The main roads along the shore are busy but from my experience traffic is non existant in the interior.
http://doorcountybiking.com/BicyclingResources.html
I always bring a bike to Road America. Lets you get around much easier. You can actually ride the track during "Tour de Road America"
http://www.pelotonride.org/
Bike Fed has some good info too.
http://bfw.org/for-your-ride/maps/