FATCA agreement between Canada and the United States
FATCA requires US persons to report to the IRS (Internal Revenue Service) the balances of all bank  accounts they hold outside of the United States every year. This is done through special forms which all US persons must file in addition to the other tax forms which such people must file every year even if they do not reside in the United States.The CRA (Canada Revenue Agency) collects this information from all Canadian banks and transfers this information to the United States.