I want to preface this by saying I'm not an expert in constitutional law; I'm a trade lawyer. But as the explanation says in the clause-by-clause guide, the Supreme Court of Canada has interpreted section 17 of the Interpretation Act to mean that in order for the crown to be bound by legislation, the legislation must say so expressly. That's what this provision does.
On June 1st, 2010. See this statement in context.