In Ontario, the doctrine of rectificationcan only be applied to testamentary instruments in limited circumstances. In Lipson v. Lipson, Patillo J. provided a summary of the circumstances in which the Court will rectify a testamentary instrument through the deletion and/or addition of words:
(i) Upon a reading of the will as a whole, it is clear on its face that a mistake has occurred in the drafting of the will;
(ii) The mistake does not accurately or completely express the testator’s intentions as determined from the will as a whole;
(iii) The testator’s intention must be revealed so strongly from the words of the will that no other contrary intention can be supposed; and
(iv) The proposed correction of the mistake, by the deletion of words, the addition of words or both must give effect to the testator’s intention, as determined from a reading of the will as a whole and in light of the surrounding circumstances.
More recently, in Robinson v. Robinson Estate (“Robinson”), the Court held that a rectification may be pursued even where the will appears clear and unambiguous on its face. In that case, the estate trustee brought an application for both interpretation and rectification. The applicant argued that the testator did not intend to revoke her 2002 will, which dealt with her European assets (the “Spanish Will”), despite the comprehensive revocation clause in her 2006 will, which dealt with her Canadian assets (the “Canadian Will”). The Court held that the equitable doctrine of rectification was not available in this case, finding that if a mistake was made, it was made by the testator in misunderstanding the legal effect of the revocation clause in the Canadian Will, rather than by the solicitor in drafting the will according to the her instructions.
Belobaba J., in so finding, offered the following summary of the law of rectification, at paragraphs 24 to 27:
24 Where there is no ambiguity on the face of the will and the testator has reviewed and approved the wording, Anglo-Canadian courts will rectify the will and correct unintended errors in three situations:
(1) where there is an accidental slip or omission because of a typographical or clerical error;
(2) where the testator’s instructions have been misunderstood; or
(3) where the testator’s instructions have not been carried out.
25 The equitable power of rectification, in the estates context, is aimed mainly at preventing the defeat of the testamentary intentions due to errors or omissions by the drafter of the will. This is a key point. Most will-rectification cases are prompted by one of the above scenarios and are typically supported with an affidavit from the solicitor documenting the testator’s instructions and explaining how the solicitor or his staff misunderstood or failed to implement these instructions or made a typographical error.
26 Courts are more comfortable admitting and considering extrinsic evidence of testator intention when it comes from the solicitor who drafted the will, made the error and can swear directly about the testator’s instructions. They are much less comfortable relying on affidavits (often self-serving) from putative beneficiaries who purport to know what the testator truly intended.
27 Here is how Feeney’s puts it:
[T]he application for rectification is usually based on the ground that, by some slip of the draftsman’s pen or by clerical error, the wrong words were inserted in the will; the mistake may be latent in the letters of instruction or other documents. Yet, when the mistake is that of the draftsperson who inserts words that do not conform with the instructions he or she received, then, provided it can be demonstrated that the testator did not approve those words, the court will receive evidence of the instructions (and the mistake) and the offending words may be struck out.
The Court of Appeal, in dismissing the appeal, emphasized that while the evidence “might give rise to speculation that the testator did not turn her mind to the effect the 2006 Canadian Will would have on the 2002 Spanish Will and the European assets” (emphasis added), a rectification could not be ordered based on the admissible evidence where the words of the Canadian Will were clear and unambiguous.
However, certain extrinsic evidence is still admissible on a rectification even where the will appears clear and unambiguous on its face, as an ambiguity may only become apparent when understood in the context of available extrinsic evidence. In the Robinson case, three parties, including the drafting solicitor, submitted affidavit evidence. The solicitor’s evidence was only that he believed that the deceased had not intended to revoke her Spanish Will, and not that he had received instructions to that effect. This evidence was therefore inadmissible. Generally, however, affidavit evidence from the drafting solicitor is a required component of an application for rectification if the lawyer is alive and capable. Other evidence, such as earlier wills and codicils of the testator, and the solicitor’s file and notes, may be admitted where appropriate.
One further issue in a rectification application is the deceased’s knowledge and approval of the contents of the will. Knowledge and approval are essential for a will to be valid, and as a point of principle, a successful rectification can only be made to a valid will. To accommodate this contradiction, the courts have consistently held that, even where a will has been read to or by a testator, a testator cannot be said to approve of an overlooked drafting error.
In Binkley Estate v. Lang, rectification was granted where the testator read the will page-by-page, but did not notice a typographical that recorded a $2,500 gift as a $25,000 gift. In Daradick v. McKeand Estate, the Court rectified a will where the drafting solicitor only alerted the testator to changes from her previous will, and the testator thus failed to notice that a clause bequeathing her home to her daughter was missing. Finally, in Welton Estate v. Haugrud, which is under appeal, the Court granted rectification where the testator failed to notice that the drafting solicitor mistakenly referred to a gift of Class “D” shares (which the testator never owned) instead of Class “E” shares after discussions with the testator’s accountant in which the shares were misidentified.
The bottom line is that testators often rely heavily on their solicitors; they may not understand the legal minutiae of a will, and cannot reasonably be expected to identify all errors within a will. As such, in Parker v. Feldgate, which has been followed by the Supreme Court of Canada, the Court held that:
If a person has given instructions to a solicitor to make a will, and the solicitor prepares it in accordance with those instructions, all that is necessary to make it a good will, if executed by the testator, is that he should be able to think thus far: “I gave my solicitor instructions to prepare a will making a certain disposition of my property; I have no doubt that he has given effect to my intention, and I accept the document which is put before me as carrying it out.” 
In sum, the Court will only rectify a will in very particular circumstances, which must include a clear mistake in the will that, absent rectification, would defeat the deceased’s testamentary intentions. The Court will not rectify a will based on speculative evidence of a testator’s intentions, or where it believes that the error was the result of a mistake by the testator in giving instructions or understanding the legal consequences thereof.
  O.J. No. 5124, 2009 CarswellOnt 7474, at 42.
 Robinson v. Robinson Estate, 2011 ONCA 493, 2011 CarswellOnt 5819, aff’g 2010 ONSC 3484, 2010
CarswellOnt 4576, leave to appeal to SCC refused 2011 CarswellOnt 14400.
 Robinson Estate v. Robinson,  ONSC 3484, 2010 CarswellOnt 4576, at 28-29.
 Robinson v. Robinson Estate, 2011 ONCA 493, 2011 CarswellOnt 5819, at 24.
 Alexander Estate v. Adams (1998),  B.C.J. No. 199 (S.C.), at 19.
 Binkley Estate v. Lang,  50 E.T.R. (3d) 44,  O.J. No. 2167 (S.C.J.).
 Daradick v. McKeand Estate, 2012 ONSC 5622, 2012 CarswellOnt 12438.
 (1883), L.R. 1 P.D. 64 (Eng. Prob. Ct.).