What is the contribution necessary in order to found a claim for unjust enrichment?

McLachlin J. then discussed the principles to be applied in assessing the contribution necessary in order to found the claim and issues of valuation as follows at paras. 27 and 31: The next question is the extent of the contribution required to give rise to a constructive trust. A minor or indirect contribution is insufficient. The question, to quote Dickson J. (as he then was) in Pettkus v. Becker, supra, at p. 852, is whether "[the plaintiff's] contribution [was] sufficiently substantial and direct as to entitle her to a portion of the profits realized upon sale of the ... property." Once this threshold is met, the amount of the contribution governs the extent of the constructive trust.... To summarize, it seems to me that the first step in determining the proper remedy for unjust enrichment is to determine whether a monetary award is insufficient and whether the nexus between the contribution and the property described in Pettkus v. Becker has been made out. If these questions are answered in the affirmative the plaintiff is entitled to the proprietary remedy of constructive trust. In looking at whether a monetary award is insufficient the court may take into account the probability of the award's being paid as well as the special interest in the property acquired by the contributions: per La Forest J. in Lac Minerals. The value of that trust is to be determined on the basis of the actual value of the matrimonial property -- the "value survived" approach. It reflects the court's best estimate of what is fair having regard to the contribution which the claimant's services have made to the value surviving, bearing in mind the practical difficulty of calculating with mathematical precision the value of particular contributions to matrimonial property. (Para. 31)