Yes, when you have your Canada eTA approved you are able to use it to enter Canada multiple times.
Your eTA is valid for five years, or until your passport expires, whichever comes sooner. Therefore
within that five years you can visit Canada numerous times usiing the same eTA.
The eTA is intended to be used for short-term visits to Canada and the limit for one visit is a
duration of six months. If you want to stay in Canada for longer than six months then you must apply
for a different type of visa.
There are other reasons as well as expiry that mean your eTA may no longer be valid, for example if
your details to any of the eligibility questions have changed. If your details have changed then you
should check that your eTA is still valid before you travel. You can check the validity and expiry
date of your eTA at any time, using the unique reference number that you were sent when you first
applied for it.