Take someone who has lived in Canada for 40 years, for example, someone who has always paid taxes in Canada, who has a residence in Canada and who has no other indicators that they are American. If American public servants feel that there are certain aspects of the file that suggest that the individual is still American, they'll ask you to transfer the file to them. I don't see how a bank, under the agreement, could have the final say over whether the file should be transferred.
On May 14th, 2014. See this statement in context.