Who chooses the mediator for a mandatory estate mediation in Ontario?

The parties themselves choose the mediator in a mandatory estate mediation, and are expected to try to agree on someone together rather than have one imposed on them. In practice, the parties (through their lawyers, if represented) typically select a mediator with relevant experience in estate, trust, or capacity disputes from the pool of qualified mediators who handle this kind of work, and agree on the mediator's fees, which the parties usually share.

If the parties cannot agree on a mediator within the applicable timeline, the local mediator roster or coordinator for mandatory mediation can appoint one, so the process doesn't stall simply because the parties disagree on who should run it. Once a mediator is selected, the parties typically also need to agree on logistics like timing, location (including whether it will be held remotely), and what materials each side will exchange beforehand so the session is productive. Choosing a mediator with genuine estate litigation experience, rather than a generalist, tends to make a real difference in whether the session leads to a workable resolution, so it's worth discussing your options with your lawyer rather than defaulting to whoever is available first.