Acutally, the Apostle Islands would be pretty nice if you have a warm enough suit. I have kayaked, and camped, up there in the past and there are a number of shallow shipwrecks that you can see from the surface. There are also many seacaves that you can paddle and swim through.
Just south of the Apostle Islands are a few lakes that are very nice for diving in. Ted may know about someof the smaller ones, but Lake Owen is one of the larger ones. She is a long thin lake that goes down about 105'. THe water is fairly clear, but there is no spearfishing allowed.
Lake Michigan and Lake Superior have many nice wrecks, bays, rock reefs and other things to freedive on. The vis is almost always 40' or more. You can spear rough fish but not panfish.
Another place to look into is Gran Maries up on Superior. The water is crystal clear and the have a huge kayak symposium up there every summer. They have a nice campground and a great little micro brewery too.
Munising Michigan is another one to look into. She is a city on a bay that is almost completly protected by a large island, Grand Island, so that you can always find protected water. It is great for kayaking and there are some nice wrecks to freedive on. They range fom a completely intact 100+ year old sailing schooner in about 25' of water to others around 65' and 90'. The kayaking is really nice as it is situated right next to the only freshwater national seashore in the country- Pictured Rocks. Imagine tall rock pillars, waterfalls and 100'+ sand dunes on a huge body of fresh water that you can acutally drink when your thristy. Water temps in August were in the mid 70's last sumeer, down t a depth of around 50'.
I don't have any shots of Superior on my computer, but here is a photo of my wife and I kayaking in Tobermorey. This place is awsome and I highly recommend it. There are wrecks in all depths ranging from sticking out of the water down to 150'. We dove a number of wrecks that started in 20' and ended in 90'. You coould always find a depth that you were comfortable with. The water was a good 72 degrees down to 60' last August. There were a lot of islands to kayak to and everything was about 30% cheaper since its in Canada.