Whoever holds a continuing power of attorney for property signed while the owner still had capacity — and if no valid one exists, nobody can sign until a court appoints a guardian, which for a home sale usually needs its own separate court approval too.
Short answer
Two routes, in order of how common they are. If the owner signed a continuing power of attorney for property while still capable, the attorney named in it can sign the sale, subject to real fiduciary duties. If no valid power of attorney exists, someone has to apply to court to be appointed guardian of property under the Substitute Decisions Act, and selling the person's home specifically then needs its own additional court approval on top of the guardianship itself.
A continuing power of attorney for property (CPOA) under Ontario's Substitute Decisions Act authorizes a sale only if the document includes that authority, and only if it was signed at the right time: "the CPOA must have been signed while the grantor had capacity; a POA signed after incapacity has set in is invalid." The attorney is not free to do as they please with the property either — they must "act in the grantor's best interests, keep detailed records of transactions, and generally avoid conflicts of interest," and selling below market value or taking a personal benefit from the deal creates real legal exposure. At closing, the lawyer will need "the original or a certified copy of the POA," will verify it meets the Substitute Decisions Act's requirements, and will register a notice of it or build the attorney's authority into the transfer document itself — start that verification early, since "title issues with POA transactions can take extra time to resolve."
If the document was never signed, was signed too late, or does not cover property, nobody can simply step in. Someone must apply to become guardian of property under the Substitute Decisions Act, which requires "evidence that your relative is incapable of managing their own property — typically including a capacity assessment," a proposed management plan for handling their finances and assets, and notice to the incapable person and other close family members. The court will also look at "whether a less restrictive option, like an existing power of attorney, could work instead" before granting guardianship, and a guardian typically has to post a bond and account for their management of the property on an ongoing basis.
Even once a guardian is in place, selling real property — especially a principal residence — is generally treated as a major decision that can require specific court approval on top of the guardian's ordinary authority. Courts scrutinize the sale closely because it is "significant, often irreversible, and directly affects the incapable person's living situation and long-term financial security," and the guardian generally has to show the sale is "genuinely necessary or clearly in the incapable person's best interests," backed by evidence such as a market valuation. Getting this wrong "can expose a guardian to personal liability or delay" the very sale the family is trying to complete — both routes take real, unpredictable time, so raise the question with the client's own lawyer the moment capacity comes up, not after an offer is signed.
See also: a case file on a power of attorney the lawyer rejected, the Certificate of Appointment of Estate Trustee, defined and what happens when a seller dies mid-deal.
Confirm which route applies before the file goes any further.
