Electronic Travel Authorization, ETA is a new requirement for foreign nationals are visa exempt and transit through Canada. This is only necessary if foreign nationals traveling to Canada. People who have a visa to Canada, Canadian citizenship or permanent residency in Canada do not need ETA documents to enter Canada. If you want to know more about the EEA citizenship then you can browse the web.
Image Source: Google
PEOPLE NEED ETA
If the individual is of any visa exempt and be given work permits or study permits, it will automatically eject the ETA when he received a work or study permit application. US citizens do not require ETA or Visa to travel to Canada. US citizens may visit Canada with a valid US passport. US permanent resident or green card holder requires an ETA for a trip to Canada and also need to carry their Green Card.
If someone is a dual citizen, he holds Canadian citizenship along with at least one nationality from another country, they do not need ETA to enter Canada. But, if he is traveling by air, they have to bring their Canadian passports. If an individual is a permanent resident of Canada, he does not need ETA Canada but needs a PR or a Permanent Resident Card or Permanent Resident Travel Document valid for travel to Canada.