Japanese maples definitely aren't fond of heat & sun. I don't know how much sun it was getting before you put up the canopy, but in your area you will want to put them somewhere that they don't get afternoon sun. Even too much morning sun in a hot climate can fry some of them--I've got mine in an area that gets sun until about noon, and some cultivars are fine but others get a bit stressed and ratty looking when we have a heat wave. I also wouldn't plant it in June--for any plant that's going to be extra stressful because it'll already be hot before it has a chance to get established, but for something like a Japanese maple that tends to "fry" a little more easily than many plants I would definitely plant it either in the fall or very early in the spring so it has a chance to get established before it has to deal with the heat. The good news is that your tree isn't necessarily dead so I wouldn't completely give up on it yet--keep it shaded as much as you can and make sure you're watering adequately and maybe it'll surprise you.
