Who has to prove the will is valid once an Ontario court orders proof in solemn form?

The person propounding the will — usually the named estate trustee — carries the initial burden of proving the will is valid once a court orders proof in solemn form. That means showing the will was properly signed and witnessed, and that the testator had testamentary capacity and knew and approved of the contents at the relevant time. Ontario courts generally start from a presumption that a will signed with the proper formalities, by a testator appearing to have capacity, is valid, which helps the propounder meet this initial burden in straightforward cases.

That presumption can be displaced. Where the person challenging the will raises legitimate, evidence-based suspicious circumstances — for example, around how the will was prepared, unusual changes in favour of the person who arranged for it, or signs the testator may not have understood what they were signing — the propounder can be required to more affirmatively prove capacity, knowledge, and approval rather than simply relying on the presumption. Separately, if the challenge is specifically that the will resulted from undue influence or fraud, the person making that allegation generally bears the burden of proving it. Because these burdens can shift depending on the facts, get legal advice early on which side of the line your situation falls.