No, I'm not talking about deadwood on maples; it's that ugly chop when someone carelessly hacked the trunk down.
I will do the cleaning and shaping with power tools, but the question is, should I do it now or wait for when the tree loses its leaves?

I would do it now. Make a nice smooth transition.Put cut-paste over the wound. Let the leader grown and we will both pay the waiting game. I am bettings yours will heal over before mine does..

Thank you, LB.
The cut paste is a must, as fungus and other issues can occur.
The smooth transition will be tried (not sure of certain success).
The waiting game will start after the next weekend.
Not sure mine will heal before yours, but I have the advantage of here being mid spring, so we have the whole growth season to hope for it.

Are you air layering that first branch, or you forgot a wrapped sandwich on the pot?

Yeah, it is a sandwich.

Here is the result.
20 minutes with the dremel, cut paste, cleaning and watering, now we wait.

Update:
That's what happens to a Trident Maple when it goes unchecked.
It goes wild.
But this is a bonus, as the cut was extensive and deep, and all this growth will help it healing faster.