How long does a Canadian eTA last?

When you have an eTA appliction approved, your authorisation to travel to Canada lasts for five years. However, it is important to note that the eTA is intended for short visits only and not for trips of any longer than six months at a time. If you are planning on visiting Canada for a period that is longer than the six months limit then you will need to apply for a different type of visa, depending on the purpose of your visit. You may need to apply for a working visa, or permanent residency for example.
One of the great advantages of having an eTA is that it allows you to travel to Canada multiple times within that five years of validity. Your eTA will only be valid if you have a valid passport and if you should renew your passport then you will also need to apply for a new eTA as your existing one will be linked to your previous passport and cannot be transferred. So your Canadian eTA lasts for five years, or until your passport expires, whichever comes first.
You can check the validity of your eTA online at any time so that you know yours is valid before you make any travel plans to visit Canada.