Had to look up what a "water maple" was - never heard that term before :-)

Larger maples tend to be rather difficult trees to grow anything under - a widespread, shallow and very greedy root system precludes a lot of opportunities. None of the suggestions you mention is ideal - what you really need to look for is something suitable for dry shade. Deadnettle or Lamium maculatum is pretty tolerant of these conditions but epimediums are the most often recommended choice. Not really very suitable for playing or walking on, however.