What is a Canadian eTA?

An eTA, or Electronic Travel Authorization, is an alternative to the usual Visa. It is similar in its purpose, however the way in which it is acquired differs.

Applying for a normal Visa can be a lengthy process however, an eTA enables you to find out if you are acceptable for travel to Canada more swiftly.

Does acquiring an eTA guarantee entry into Canada?
How long does the eTA remain valid for?
Who needs to apply for an eTA?
Can children travel on the same eTA as the parent/s?
What do I need to apply for a Canada eTA?
Is it important to obtain a Canadian eTA?