In this case, the person is interested in a Flight Attendant position and is not a Canadian citizen (and therefore does not have a Canadian Passport) but would have Canadian Permanent Residency and is therefore legally entitled to work in Canada. The Air Canada and Rouge website stipulate that applicants MUST have a valid Canadian passport, and the answer to a follow up was that this is due to visa requirements to some of the countries which may be operated to, which seems strange to me. Countries like the United States issue crew visas to eligible foreign airline crews; I work at a foreign (overseas) airline employing crews of pretty much every nationality you can imagine and all other countries we've ever flown to allow the crews to enter with minimum fuss on a General Declaration. I know that foreign authorities' applications of this can be somewhat inconsistent from airline to airline-- my airline enters Russia and China on General Declarations while my former airline's colleagues are required to have visas for these countries. But that's about it.
Does Air Canada have the same requirements for Pilots? I recall, many years ago, applying for my Restricted Area pass in Toronto and seeing another pilot pull out his French passport with his Permanent Resident card.
-President Ronald Reagan
I became an AC FA in 2005, which was the last year that AC hired permanent residents for the flight attendant position. The problem was with Chinese passport holders that ended up not being allowed to fly to china while working for a Canadian carrier. This debacle prompted the change in hiring requirements from my understanding. Likely it is something that could be challenged if someone wanted to persue it, since as you mentioned a foreign passport holder could apply for crew visas from every country that AC flies to (an expensive undertaking, but several in my initial course did just that).