What is the test for granting public interest standing in a civil case?

In Canadian Council of Churches v. Canada (Minister of Employment and Immigration), 1992 CanLII 116 (SCC), [1992] 1 S.C.R. 236 at paras. 35 and 36, Cory J. commented that a balance must be struck between ensuring access to the courts and preserving judicial resources. As the purpose of granting public interest standing is to prevent immunization of legislation from challenge, if the legislation is or will likely be subject to attack by a private litigant, public interest standing need not be granted. The decision whether to grant public interest standing is discretionary but the applicable principles are to be interpreted in a liberal and generous fashion in exercising that discretion.