I'm sorry, I was seeking to answer that in the second part of my response.
A U.S. citizen is not currently subject to any reporting requirement, because citizenship isn't relevant, as residence is, for Canadian tax purposes. Where a person shows a marker of having a U.S. indicator, perhaps citizenship, then the bank or the other financial institution in question will generally, one would think, be asking for follow-up to verify whether or not that person is actually a U.S. taxpayer. By virtue of that inquiry, they practically or often have the knowledge, but there's not a separate requirement to that effect.