I wonder if something smaller and less dramatic than maple or cottonwood might work with the scale of the yard. Apricot trees will sometimes get lovely fall color and can easily be kept small, for example. But if fruit is a problem, I've seen some locust trees that produce very light shade that would be great to garden underneath. And they nitrify the soil. I expect neither will take a huge amount of excess water - no more care than you give roses. But I suppose root competition is something to look out for in any choice of a tree.
