I don't know about the Japanese maple, but my parents had a flowering cherry in the yard for many years. This tree is susceptible to mid-summer leaf drop caused by excessive temps. You can prevent this by selectively pruning interior shoots. This will allow better air circulation in the canopy that will help keep temps down. As with any flowering tree/shrub, pruning should be done after the flowers have fallen off.
Cherry trees are also magnets for tent moth caterpillars. A small colony can completely defoliate a small tree, so keep an eye out for their tell-tale nests - see pics here: The Eastern Tent Caterpillar
Destroy the silken nests and watch the birds feast on the exposed caterpillars.