Can co-executors act separately in Ontario?

It depends. Whether one co-executor can act without the others turns on what the will says and on the law, so it is worth confirming with a lawyer before you act alone. Once the other trustees are no longer in office, joint powers given to two or more trustees may be exercised by the survivor or survivors of them for the time being.

If co-executors disagree, they can apply to the court, without starting an action, for its opinion, advice or direction on managing the estate. A trustee who follows that direction is treated as having discharged their duty, unless there was fraud, wilful concealment or misrepresentation.

If the deadlock cannot be fixed, the Superior Court of Justice may remove an estate trustee on any ground on which it may remove any other trustee and appoint another proper person. A person named as executor does not have to act, and one who renounces probate has no rights as executor, with administration proceeding as if they had never been appointed, but an executor who has already started acting cannot use the Trustee Act's out-of-court retirement procedure and generally needs a court order to step down.