RV Site UP Michigan - Finger Lakes

I would wait to go to the UP mid to late July. Still can be cold and rainy earlier than that.
I would stay around Munising. We stayed at Munising Tourist Park Campground right in the lake. They do have lake front sites.

While a bit west of the finger lakes, Letchworth State Park is worth a visit. 150 miles southeast of Letchworth is Ricketts Glen State Park in PA. 21 waterfalls along a 7 mile hike.

If you're going thru Wisc to the UP do your self a favor and stop at Little Girls Point County Park. Want to see the great lake? You'll be camped on its shore. Electric only. No water to speak of, nor dump. Gravel sites, no showers, pit toilets. But lovely.

Another NY SP is Sampson State Park

Are you going to Michigan or New york?

If you are camping near Lake Superior take an extra sweatshirt or two. The wind can be quite cool off of the lake.

Lots of choices.

There's a state park that is highly rated just over the bridge

Picture rocks
Taquamana falls
Procupine
Copper harbor

Take M26

Can take a boat over to Isle Royale

Go over to Mackinac Island

Mackinaw City just on the south side of the bridge

Sampson is a nice park. In the immediate area are a plethora of Wineries, and distilleries. The former Seneca Army Depot has White Deer tours,The LDS church has the Peter Whitmore Farm in Waterloo if you are interested in the history. Geneva has become somewhat of a foody destination.
Taughannock Park is also a nice park although older and tighter than Sampson. Has the highest single drop falls East of the Rockies. Ithaca with Cornell is 8 miles South.

Van Riper on the east side of Lake Michigamme off U.S. 41 between Marquette and L'Anse is nice campground. Another nice one is Muskallonge Lake north of Newberry. It sits on the north side of Muskallonge Lake and Lake Superior is a short walk across the road

McLain State Park. You can watch the sunset over Lake Superior.