This question assumes that this citizen has another passport (eg from dual citizenship). I thought to ask because identical questions for different countries yielded disparate answers. Both of the following quotes can be found in the penultimate para in each answer. If existent, please cite official sources.
The previously accepted answer is out of date.
As at the time of writing (November 2018) the Canadian Government says this:
Dual Canadian citizens can no longer travel to or transit through Canada by air with a non-Canadian passport. You need a valid Canadian passport to board your flight.
There is an exception for Canadian-American citizens:
Exception: If you are an American-Canadian dual citizen with a valid U.S. passport, you don’t need a Canadian passport to fly to Canada. However, you will still need to carry proper identification and meet the basic requirements to enter Canada.