What is the burden of establishing that the law is unconstitutional?

A person challenging the constitutionality of a law has the burden of establishing that the law is unconstitutional. That burden has been described as a “presumption of constitutionality”: see e.g. Ernst v. Alberta Energy Regulator, 2017 SCC 1, [2017] 1 S.C.R. 3, at para. 21.

Where the person challenging the constitutionality of a law fails to provide an adequate factual basis upon which to decide the challenge, the challenge fails: Ernst, at para. 22. The lack or absence of the requisite factual basis “is not just a technicality that [can] be overlooked, but rather it is a flaw that is fatal to the [challenging party’s] position”: Mackay v. Manitoba, 1989 CanLII 26 (SCC), [1989] 2 S.C.R. 357, at p. 366.