Nofa93, welcome to the site.
Your little maple has had a rough go of it. I must confess, I would be considering removal. What I see is callus growth producing woundwood but a whole lot more canker. If there were a great deal of callus growth that had produced woundwood with no active pathogen that appeared to be growing faster than the callus then that would be a different story. We have all seen the examples of trees with huge holes, standing for literally centuries. But I don't see that here. The decay we are seeing could be saprophytic only, but the perennial canker is another issue compounding the problem.
I also don't see many options for making the tree's situation better. There is nothing to cable or brace that would mitigate the damaged area or make the tree stronger. Removing the rock and mulching would be excellent ideas, however, that is also not going to solve the problem in this particular situation. The damage has occurred and the tree is not being able to overcome it. So in my mind, why wait? Remove and replant with a suitable and attractive specie.
I am not a big fan of planting a replacement tree prior to the removal of another tree in this crowded of a situation. The competition for light, nutrients and space can inhibit development in the formative years that are so important.
Personally, there is nothing wrong with Norway maples if grown in a suitable environment. You do not say where in Canada you are, but here in a Zone 4 we experience a great deal of rib fracturing on the Norway maple, due to the winter temperature fluctuations, but they survive this phenomena well. If in too hardy of a zone, these trees become invasive. But they have many cultivars that are attractive and hardy and fill a need for those of us living outside the hardier zones where there is more to choose from.
Sylvia