The Ontario Court of Appeal’s recent decision in Seguin v. Pearson, 2018 ONCA 355 provides guidance to estate practitioners regarding the complex law surrounding undue influence. Specifically, this appellate decision draws a clear distinction between the probate and equitable doctrines of undue influence which are often misunderstood by counsel. The Court states:
 […] The rebuttable presumption of undue influence arises only in the context of inter vivos transactions that take place during the grantor’s lifetime. It arises from particular relationships when the validity of inter vivos dispositions or transactions is in issue; once the presumption is established, the onus shifts to the transferee to rebut the presumption: Banton v. Banton (1998), 1998 CanLII 14926 (ON SC), 164 D.L.R. (4th) 176 (Ont. Ct. (Gen. Div.)), at p. 209.
 In the case of wills, it is testamentary undue influence, amounting to outright and overpowering coercion of the testator, which must be considered. The party attacking the will bears the onus of proving undue influence on a balance of probabilities: Vout v. Hay, 1995 CanLII 105 (SCC),  2 S.C.R. 876, at p. 887; see also Neuberger v. York, 2016 ONCA 191 (CanLII), 129 O.R. (3d) 721, at paras. 77-78.
This case clearly enunciates what doctrine should be applied and when, thus remedying any ambiguity on the topic. Check it out: http://canlii.ca/t/hrghl