It depends.
If you apply for an initial work or study permit before you travel to Canada
You will get an Electronic Travel Authorization (eTA) automatically once your work or study permit application is approved. You don’t need to apply for an eTA or pay extra fees. Your eTA number will be included in the letter of introduction we will send you when your study or work permit is approved. Keep this number in case you need to contact us about your eTA.
If you plan to apply for an initial work or study permit at a Canadian port of entry
Depending on your method of travel:
by air: you need to apply for an eTA before you can board your flight to Canada;
by car, bus, train or boat (including cruise ship): you don’t need an eTA.