If there are multiple estate trustees, do they all have to agree before selling estate property in Ontario?

Generally, yes. Where a will names more than one estate trustee, or more than one person is appointed as trustee where there's no will, the default rule is that co-trustees must act jointly and unanimously when exercising a discretionary power like selling estate property, unless the will itself says otherwise. This reflects the broader principle that trustees hold their authority together, as a single decision-making body, rather than each having an independent power to act alone on behalf of the estate.

Some wills anticipate this and expressly allow decisions to be made by a majority of the trustees, or delegate specific authority to fewer than all of them, which changes the default rule for that estate. Where the will is silent and trustees genuinely can't agree on whether or how to sell a property, the disagreement can become a real obstacle to progressing the estate, sometimes requiring an application to the court for directions to break the deadlock. A buyer's or lender's lawyer will also typically want to see that all necessary trustees have signed relevant documents, so a sale can effectively stall if even one trustee refuses to cooperate. Anyone acting as a co-trustee facing disagreement with the others should get legal advice on the options before the impasse delays the estate further.