I stayed at the Straits SP lower campground (sites # 52 to #117) on the northside of the Mackinac Bridge a very nice park. The other portion of the lower campground is not as level and some sites could be hard to get into. There are campsites that have a view of the bridge but no hook ups. It's just on the edge of St. Ignace. Be sure to stay a couple of nights and take the ferry to Mackinac Island. If you have a bike take it. It's a great place to spend the day.
As far as the Apostle's, I stayed at Dalrymple Muni Park just north of Bayfield. The sign is a little hard to see on the right just after you top out on a hill. The sites are first come first served with about 6 or 7 sites right about the water and a view of Madeline Island. I stayed in site #23 (beautiful view) next to another site which had a 4 outlet electric hookup so I ran an extension cord to it. There are a couple other sites that have electric down by the water. As far as water hookups there are none but you could run a long hose to the site I was in or the one next to mine and to fill your tank. There are several common water spigots throughout the park.
It's a ways from the Mackinac Bridge to Bayfield. A nice place to stay is Munising, UP MI muni campground, just west of town. I stayed in the overflow area with water and electric. It was nice because I didn't have direct neighbors which I would have had in a regular campsite. There are campsites right at the beach area but I imagine they are hard to come by. On the east edge of Munising is an entrance to Pictured Rocked Nat'l Lakeshore.
Joy A. & Olive
and "Puff", too