Canada (Attorney General) v. Fairmont Hotels Inc., 2016 SCC 56:
Rectification is an equitable remedy designed to correct errors in the recording of terms in written legal instruments. It is limited to cases where a written instrument has incorrectly recorded the parties' antecedent agreement. In other words, rectification is not available where the basis for seeking it is that one or both of the parties wish to amend not the instrument recording their agreement, but the agreement itself.
Where the error is said to result from a mistake common to both or all parties to the agreement, rectification of the instrument is available upon the court being satisfied that there was a prior agreement whose terms are definite and ascertainable; that the agreement was still in effect at the time the instrument was executed; that the instrument fails to accurately record the agreement; and that the instrument, if rectified, would carry out the parties' prior agreement.
It falls to a party seeking rectification to show not only the putative error in the instrument, but also the way in which the instrument should be rectified in order to correctly record what the parties intended to do. The applicable standard of proof to be applied to evidence adduced in support of a grant of rectification is the balance of probabilities. A court will typically require evidence exhibiting a high degree of clarity, persuasiveness and cogency before substituting the terms of a written instrument with those said to form the parties' true intended course of action. On rectification, both equity and the civil law are ad idem, despite each legal system arriving at it by different paths — the former being concerned with correcting the document, and the latter focusing on its interpretation. This convergence is undoubtedly desirable.