What is the legal test of undue influence in the context of a Will?

When considering the issues of testamentary capacity and undue influence, the leading decision of Vout v. Hay, 1995 CanLII 105 (SCC), [1995] 2 S.C.R. 876 laid down the principles which were summarized neatly by Cullity J. in Scott v. Cousins (2001), 37 E.T.R. (2d) 113 at para. 39 as follows: 1. The person propounding the will has the legal burden of proof with respect to due execution, knowledge and approval and testamentary capacity. 2. A person opposing probate has the legal burden of proving undue influence. 3. The standard of proof on each of the above issues is the civil standard of proof on a balance of probabilities. 4. In attempting to discharge the burden of proof of knowledge and approval and testamentary capacity, the propounder of the will is aided by a rebuttable presumption. Upon proof that the will was duly executed with the requisite formalities, after having been read over to or by a testator who appeared to understand it, it will generally be presumed that the testator knew and approved of the contents and had the necessary testamentary capacity. 5. This presumption simply casts an evidential burden on those attacking the will. 6. The evidential burden can be satisfied by introducing evidence of suspicious circumstances -- namely, evidence which, if accepted, would tend to negative knowledge and approval or testamentary capacity. In this event, the legal burden reverts to the propounder. 7. The existence of suspicious circumstances does not impose a higher standard of proof on the propounder of the will than the civil standard of proof on a balance of probabilities. However, the extent of the proof required is proportionate to the gravity of the suspicion. 8. A well-grounded suspicion of undue influence will not, per se, discharge the burden of proving undue influence on those challenging the will: …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.