Interac e-Transfers are only available in Canada for individuals who have Interac-partnered bank accounts (most of them). So, no you cannot use Interac e-Transfer in the U.S. That being said, Interac does have a collaboration with Mastercard and Western Union to allow Canadians to send International Transfers.
Interac Debit is made to be a simple, secure, and easy way to pay for your everyday purchases, and is accepted across Canada and approximately 2 million retailers in the United States.
