Travelers risk being turned away at U.S. customs , as entry rules come into effect . Canada allows short - stay residents under the visa waiver program entry to the U.S . Visitors must submit documents online at least three days before they enter .
Travelers risk being turned away at U.S. airports , as entry rules come into effect . ESTA allows short-term visitors under the visa waiver program entry to the U.S . Visitors must register details online at least three days before they depart .