Try this:
A: Pick one sucker that is positioned well (pointing up, solid part of the stump.)
B: drill a hole in the stump, and put a stake in it. Use this stake to straighten up that one sucker if needed.
C: Cut the tips off of all the other suckers so they are a foot below your favoured one.
D: If there are others that are trying for vertical, weigh them down with pop bottles full of sand or water to make them closer to horizontal.
E: A year from now in August, take off half the suckers, and again tip prune any that are trying to be the top.
F: Two years from now in August, remove the remaining suckers.
The idea: With a lot of vertical suckers, no one will establish apical dominance. Taking off the growth tips, and forcing them to a less vertical angle, increases the chances that one will dominate.
By leaving the extra suckers on for another summer, you are feeding the root. Right now you have a lot more root than you have top. Taking all the suckers off now may result in too much root dying at worst, or at best slowing the growth of your new tree.
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Silver maple are known for being weak trees. The recovering tree will have a major weakness at the point where the new trunk joins the old stump. This is a 10-20 year temporary solution.
This would be a good time to move over a space, and plant a permanent replacement -- maybe a red maple or sugar maple. The sugar maple will give you a quick tree, growing 4-5 feet a year if you are in a zone 5 or so climate. The hard maple will grow at a third the speed, but when it gets big enough to take over, you can take out the silver maple, and you now have a tree that will last generations.
Put the new tree a reasonable distance from the silver. You want the new guy to get to be 20 feet or so whlle the silver is getting to 40. Place it where it won't get shaded by the faster silver.
