“The parties agree that, when determining whether to grant leave to intervene under r. 13.02 Rules of Civil Procedure, the court must consider:
a. The nature of the case;
b. The issues that arise in the case; and
c. The likelihood that the proposed intervener will be able to make a useful contribution to the resolution of the appeal without injustice to the immediate parties: see, e.g., Jones v. Tsige, 2011 CanLII 99894, 106 O.R. (3d) 721 (C.A.), at para. 22, Peel (Regional Municipality) v. Great Atlantic & Pacific Co. of Canada Ltd., 1990 CanLII 6886, 74 O.R. (2d) 164 (C.A.).
…
Courts have identified several principles that apply when considering whether a proposed intervener may make a useful and distinct contribution to a proceeding:
a. The proposed intervener must have a real, substantial and identifiable interest in the subject matter and a distinct perspective to be articulated that is different from that of the parties: Craft et. al. v. City of Toronto et. al., 2019 ONSC 1151, 302 A.C.W.S. (3d) 499, at para. 63;
b. The likelihood of intervention is a function of many variables including, but not only, the experience and expertise of the proposed intervener: Jones, at para. 25;
c. The proposed intervener must offer something more than the repetition of a party’s argument, though some overlap may be permitted: Craft, at para. 62, Halton, at para. 45.
d. It is desirable to have all relevant possibilities brought to the court’s attention, including submissions on the impact of its judgment. This is true even where the intervener may bring only a slightly different perspective to be considered: Craft, at para. 64.
e. The fact that the position of a proposed intervener is generally aligned with the position of one of the parties is not a reason to deny it leave if the proposed intervener can make a useful contribution to the analysis of the issues before the court: Seaduto v. Cucu, 2017 ONCA 224, 227 A.C.W.S. (3d) 283, at para. 11.”