Can a Joint Account Holder Be Forced to Share the Money With the Estate in Ontario?

Sometimes, yes. Under Pecore v. Pecore, 2007 SCC 17, the presumption of resulting trust is the general rule for gratuitous transfers, so an adult child added to a parent's account without paying is presumed to hold it in trust for the parent and, on death, for the estate. The person receiving the transfer bears the onus of showing a gift was intended.

Courts may look at the wording of the bank documents, control and use of the funds, a power of attorney, the tax treatment of the account, and later evidence if relevant to the parent's intention at the time of the transfer. Financial dependency of an adult child does not create a presumption of gift, though it can be strong evidence against the trust. Survivorship rights vest when the account is opened, so the gift is made during life, and what is gifted is the survivor's interest in the balance at death.

Between spouses, money on deposit in both names is deemed held as joint tenants. Joint deposits can also count toward a dependant support claim, but only the portion that belonged to the deceased. Outcomes depend on the facts, so get legal advice.