I am very partial to Michigan of course because I live here but our northern Michigan is excellent in the summer, it can get hot here but not steamy like so much of the nation and there's always a cool stream, river, lake to dip into to cool off. I just got back from scouting out a gorgeous route around the "tip of the mitt" going from Charlevoix to Mackinaw City and if that isn't enough you can take the ferry to the NO automobile island and ride there too. There are several trails that run the length, north and south of the state, right up the middle and along the coast lines of the Great Lakes. This route I checked out connects several coastal towns and offers riding along the lakeshore and through the "tunnel of trees" for 20 miles of heavily canopied narrow winding roads. I have a friend who pedaled the entire coast of Michigan over 1,500 miles and did an online log of his trip. I'll find the link and post it here.