Does it matter whether spouses signed a formal domestic contract versus an informal agreement for estate claims?

Yes, it matters a great deal. A properly executed domestic contract — a marriage contract, cohabitation agreement, or separation agreement that meets Ontario's formal requirements — is generally far more likely to be enforced when it comes to releasing claims against an estate than an informal or undocumented understanding between spouses or partners. Ontario family law gives specific legal effect to validly signed domestic contracts, which gives a court something concrete to rely on when deciding whether a release of estate claims should stand.

An informal arrangement — a verbal understanding, an unsigned draft, or a casual email exchange — gives a court far less to work with. Without proper execution, there's more room to argue about what was actually agreed, whether both people understood what they were giving up, and whether the "agreement" was ever really finalized at all. That uncertainty makes informal arrangements considerably harder to rely on, whether you're the person hoping to enforce a release or the one hoping to challenge it. If estate claims matter to you, putting the agreement in proper written, signed form — reviewed by a lawyer — is the difference between a release a court can act on and one it may simply set aside.