Some people are exempt from applying for visitor visas. If you are one of the following nationals, you can apply for an ETA:

AndorraFranceMaltaSolomon Islands
BahamasHong Kong Special Administrative Region of the People’s Republic of China (Must have a passport issued by Hong Kong SAR)NetherlandsSwitzerland
BarbadosHungaryNew ZealandTaiwan (Must have an ordinary passport issued by the Ministry of Foreign Affairs in Taiwan that includes the personal identification number)
BelgiumIcelandNorwayUnited Arab Emirates
Brunei DarussalamIrelandPapua New GuineaUnited Kingdom
BulgariaIsrael (Must have a national Israeli passport)PolandBritish National (Overseas)
ChileItalyPortugalBritish overseas citizen (re-admissible to the United Kingdom)
CroatiaJapanRomania (Electronic passport holders only)British overseas territory citizen with citizenship through birth, descent, naturalization or registration in one of the British overseas territories of: Anguilla, Bermuda, British Virgin Islands, Cayman Islands, Falkland Islands (Malvinas), Gibraltar, Montserrat, Pitcairn Island, Saint Helena, Turks and Caicos Islands
CyprusRepublic of KoreaSamoaBritish Subject with a right of abode in the United Kingdom
CzechiaLatviaSan MarinoPermanent Residents of the United States
DenmarkLiechtensteinSingaporeVatican City State, (Must have a passport or travel document issued by the Vatican)