Just follow the law. A little reading and a quick search at the LTB website gives you the answers.
If the tenant didn’t give notice that they were leaving, but the landlord believes the tenant has left the rental unit - can the landlord change the locks and re-rent the unit?
The landlord should make a reasonable effort to contact the tenant to determine if they have in fact left the unit (for example, by writing the tenant or calling them, if the landlord has the tenant’s number).
If the landlord believes that the tenant has abandoned the rental unit, then the landlord may apply to the Board for an order ending the tenancy. Although this is not mandatory, if the landlord re-rents the unit without having the Board confirm that it is abandoned in an order, and the tenant has not really left, the tenant could take legal action against the landlord.
The application form that landlords can use is the Application to Terminate a Tenancy and Evict a Tenant (Form L2).
What can a landlord do with property that is left in the unit after the tenant has moved out or has been evicted?
This depends on a number of things such as how and when the tenant moved out, and why they moved out. There are special rules a landlord must follow before disposing of abandoned property. For information about the rules, you should contact the Landlord and Tenant Board.
And since you have a termination notice if you want to go after them for more rent arrears caused by them leaving without notice is dictated by section 88 of the RTA.
Basically 10 days from "the date the landlord knew or ought to have known that the tenant had vacated the rental unit". Of course this does not absolve you from the need to minimize losses as well by re-renting the unit.