eTA is issued to citizens of visa-exempt countries who intend to visit Canada, and are expected to have applied for and obtained eTA prior to their departure.
The following class of foreign nationals are visa or eTA exempt.
U.S. citizens
U.S Lawful Permanent Residents
Travellers with a valid Canadian visa
Other exceptions
Canadian citizens, including dual citizens and Canadian permanent residents do not need to apply for an eTA or a visa to enter Canada.