U.S. citizens are exempt from the eTA requirement and must carry proper identification such as a valid U.S. passport. Lawful permanent residents of the United States who hold valid status in the U.S. are exempt from the eTA requirement.
Who already have a visa in their passport. Travelers may wish to avoid buying plane tickets until they have obtained an ESTA (or a valid visa, in case the ESTA is not approved). ESTA applications may be submitted at any time prior to travel. The processing of an ESTA can take up to 72 hours.