What is the burden of proof against fraud and undue influence against a Will?

In Vout v. Hay, 1995 CanLII 105 (SCC), [1995] 2 S.C.R. 876 Sopinka J.A. said at para. 28 the following: Accordingly, it has been authoritatively established that suspicious circumstances, even though they may raise a suspicion concerning the presence of fraud or undue influence, do no more than rebut the presumption to which I have referred. This requires the propounder of the Will to prove knowledge and approval and testamentary capacity. The burden of proof with respect to fraud and undue influence remains with those attacking the Will.