What is the test for constructive trust in the context of a claim for unjust enrichment?

McLachlin J. summarized at para. 31 as follows: 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 [page1000] 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 the family property.