A systemically important bank is a categorization and a nomination by the Superintendent of Financial Institutions. The superintendent, under law, will have the power to nominate or declare which institutions are deemed to be systemically important. In Canada, the superintendent has already so declared that our six major banks are deemed to be sufficiently systemic in nature, so that their failure would pose harm to the Canadian economy, and therefore, they would be subject to additional supervisory requirements. In this case, under the act, they would be subject to the bail-in regime. The determination is multifold, it's made by the superintendent, and it's consistent with international practices.
On May 18th, 2016. See this statement in context.