Landlords are allowed to state in their rental agreements smoking is not allowed on the property. However, if a tenant does not comply with this you will still have to prove that the smoking is causing a problem such as other tenants complaining, or if there’s allergies or medical conditions that are aggravated by the smoke. At that point you can issue the tenant with a notice which still gives them an opportunity to correct the situation before you can take the matter to the Landlord and Tenant Board.
For more resources on developing rules and policies prohibiting smoking indoors, visit https://smokefreehousingon.ca/