What can I do if the seller promised vacant possession but the tenant refuses to leave before closing?

If your Agreement of Purchase and Sale made vacant possession a genuine obligation of the seller and the seller cannot deliver it, the seller is generally in breach of that promise, separate from any issue between you and the tenant directly. Your options typically include negotiating a short delay to allow more time for the tenancy issue to resolve, closing anyway and pursuing the seller separately for the loss caused by the broken promise, or, if the failure is serious enough and your agreement supports it, treating the seller as in default and pursuing remedies such as damages.

Because Ontario tenants have real, enforceable rights under the Residential Tenancies Act, 2006, a seller cannot simply remove a tenant on short notice regardless of what was promised to you, and the timeline for a dispute at the Landlord and Tenant Board does not bend to your closing date. Get your lawyer involved as soon as it looks like vacant possession will not happen on schedule, since your realistic options narrow considerably the closer you get to the closing date itself.