Is mediation available for a will dispute even if it's not mandatory outside Toronto, Ottawa, and Windsor?

Yes. Outside the Toronto, Ottawa, and Essex County regions, where mediation is mandatory, parties to an Ontario estate or will dispute can still choose to mediate voluntarily at any stage, and there's nothing stopping them from doing so simply because their court region doesn't require it. Courts generally encourage voluntary mediation in these cases, given how often estate disputes involve ongoing family relationships that a purely adversarial court process can strain further.

In practice, voluntary mediation works essentially the same way as mandatory mediation: the parties agree on a mediator, share the relevant documents, and attend a session (or series of sessions) aimed at reaching a resolution without a trial. The main difference is timing and flexibility — without a mandatory deadline forcing the issue, voluntary mediation can happen earlier, before a lot of legal costs are incurred, or later, once the parties have a better sense of the evidence and are more motivated to settle. If you're in a will dispute outside a mandatory-mediation region and think a negotiated resolution might be realistic, raise voluntary mediation with the other side and your lawyer early, rather than assuming a trial is the only path forward.