Starting March 15, 2016, visa-exempt foreign nationals who fly to or transit through Canada, including visa-exempt British Citizens, will need an Electronic Travel Authorization (eTA). Exceptions include U.S. citizens and travellers with a valid visa.

Entry requirements for other methods of travel (land, sea) have not changed.

To apply you must have a valid passport, a credit card (Visa, MasterCard, American Express, or a pre-paid Visa, MasterCard or American Express), and email address. It costs $7 CAD to get an eTA. It will be valid for up to five years.

UPDATE: Until September 29, 2016, travellers can board their flight WITHOUT an eTA if they have the correct travel documents such as a valid passport. More information here: http://www.cic.gc.ca/english/helpcen...um=1235&top=16

The official eTA application site can be found here:

http://www.cic.gc.ca/english/visit/eta-start.asp

Guidance on completing the documentation can be found here:

http://www.cic.gc.ca/english/pdf/eta/english.pdf