I would try to peel as much loose bark off as possible in order to let it dry underneath and prevent wood rot. Use a screwdriver, but try not to cut into live tissue. The objective is to keep the exposed heartwood dry. Do not apply tree paint as that will hold in moisture which you want to prevent.
If it is canker, it may get progressively worse......or not. The tree will self repair to some degree during the growing season - the callous rolls around the top of this wound are evidence that the tree is actively trying to repair the area. However, it is during the dormant season that the canker may advance.
If you really love the tree, you can have an arborist inject a fungicide once a year which will be taken up into the living tissues of the tree and hold the canker in check, but will never totally eliminate it. The other issue with an injected fungicide is that any seeds the tree produces will have traces of the fungicide which can be passed up the food chain by wildlife, so you need to weigh the environmental aspects. I more envoro-friendly option would be to have a deep feeding done which will keep the tree robust and therefore help the tree fight the canker. Both of these services can be expensive, so you need to weigh your love for the tree against your budget.
At any rate, it doesn't hurt to consult with a reputable arborist to get their opinion.