Best to move it in the fall. Where the branches end, that's the drip line so start digging around the tree and it depends how deep the roots but since it's only three years old probably not more then two feet, that's a guess. When you have the root ball and it can be rocked with the shovel, not holding onto the stem, you can shave the diameter of the ball off until you hit roots.

Here is a link that might be useful: Propagating Perennials

You might want to find out which maple it is. You do not want silver maple or norway maple in your yard at all.... They are hated by many people...

I moved a young maple tree last summer. I moved it in late spring before it got hot. It had only been in place for a year so the roots hadn't grown much from its original root ball. Throughout the summer it lost most of its leaves and didn't seem to start growing new leaves until fall; just as all the trees were shedding. With an entire growing season lost I was concerned it wouldn't make it through the winter, but right now its buds are opening and it has tons of growth. I've also been told that you should dig at the drip line when removing a tree. Sounds like you may have a norway maple. These seem to be pretty tough trees. good luck.

Sounds more like a red maple than a Norway, but that is a wild guess since I know nothing of it or where you are located.
If it is very small (about 2 to 3 feet tall or so) you probably have a good chance of moving it even with leaves already out. If the soil is compact enough to dig it out without the root ball falling apart I'd go for it. Dig about a foot down and eighteen inches for every inch of trunk diameter.