Certainly the eligibility of the Canada mortgage bond as a high-quality liquid asset makes it a more attractive thing for banks to hold. That said, if Canada mortgage bonds or other government-guaranteed securities were not considered high-quality liquid assets, banks would have to hold other types of high-quality liquid assets, which might be government debt, so it's not obvious that one is better than the other.
On May 21st, 2020. See this statement in context.