I have decided to plant one of the above--Kousa dogwood, Amur maple,
Trident maple, or Triflorum maple--in my front yard as the "featured"
tree. It is important that the tree have a single trunk, ideally 4 to 6
feet off the ground. Which of these would I likely have the best luck
with training to have a single trunk? Are there specific cultivars that
achieve this?

Thanks.