If it suckers below the graft you NO LONGER have sunset maple and no way to tell what you have ( I assume thast is what you mean by suckering )....in that case torch it ...if above the graft pick the biggest branch and cut others and train up. David

If the sunset maple you are talking about is a Red Sunset, then the "suckering" will also be Red Sunset. Cultivars of the red maple (Acer rubrum) are either propagated from tissue culture or cuttings. Commerical grafting of red maples isn't done due to problems between the graft and root stock. The area that looks like a graft union is actually where the nursery cut the tree back to force a straighter trunk. Let the "suckering" go until next spring, after they leaf out, keep the straightest one, cut back the rest.