National Parks June/ July... A/C needed?

The only park I would question would be Canyonlands. That will be your hottest spot. Where are you staying there? Dead Horse Point State Park? Some of the sites do have tall junipers which will provide shade depending on the direction of the sun. Also, some have covered picnic tables. Bring folding lounge chairs and find a shady spot in 'your yard' for your nap or lunch. There are also many nice campgrounds along the Colorado River on Hwy 128. They all have shade - big cottonwoods. However, for it and all the other parks if you have a site with a tree you'll be just fine. Even at Grand Canyon, if you're staying at Mather or Desert View, there will be shade, especially Mather. Personally, I wouldn't buy a generator for the short time you'll be at those areas. They will all definitely cool way down at night!

Here's a site that shows campsite photos. Perhaps your chosen parks are on this site so you can see what's ahead:

http://www.campsitephotos.com/campground/Dead-Horse-Point-State-Park