eTA is a means for entering Canada officially required by citizens of certain countries that are Visa exempt (TRV not required). Such foreign nationals require an eTA prior to boarding their flights for Canada, but if the said, visa-exempt travelers, enter Canada by road or by sea then the requirement for an eTA also gets waived. The list of these Visa-exempt countries is subject to change from time to time and can be found on the “www.canada.ca” website