What is the legal test for establishing a common law argument in a discrimination case?

In particular, with respect to my review of the Respondent’s common law argument the guidance in Law v. Canada (supra) is as follows as p. 39: The equality guarantee is a comparative concept, which ultimately requires a court to establish one or more relevant comparators. The claimant generally chooses the person, group or groups with whom he or she wishes to be compared for the purpose of the discrimination inquiry. However, where the claimant's characterization of the comparison is insufficient, a court may, within the scope of the ground or grounds pleaded, refine the comparison presented by the claimant where warranted. Locating the relevant comparison group requires an examination of the subject-matter of the legislation and its effects, as well as a full appreciation of context.