What can I do if the former owner or a tenant refuses to leave a property I bought at a municipal tax sale?

A municipal tax sale does not come with any guarantee of vacant possession, and dealing with a remaining occupant afterward generally requires its own legal process rather than a quick fix. What that process looks like depends heavily on who is there and why. If the former owner has simply stayed put with no legal right to remain, you would generally need to pursue a court application for possession, since self-help removal is not a safe or lawful option in Ontario.

If a genuine tenant is living there, the picture is different again - a related question covers this specifically, but in short, a bona fide tenancy is not automatically ended by the change in ownership, and ending it properly means following Ontario's residential tenancy rules rather than treating the tax sale itself as an eviction.

Because this can take real time and cost after you already own the property, ask what is known about occupancy before bidding, and speak with a lawyer promptly after closing if someone is still there, rather than attempting to resolve it yourself.