You cannot really do maintenance work as involved as painting so close to the end of the tenancy, so you will have to wait until the property is empty before cleaning thoroughly and painting it.

During the tenancy, you would have had many opportunities to do a maintenance inspection and raise the problems that you discovered at those times. It may or may not be worth filing for the damages at the Landlord and Tenant Board before they leave, using an L2 application, but again, there is no guarantee that you can collect even if you are successful. The form and instructions are available here: https://tribunalsontario.ca/ltb/forms/