Agreed. The citizenship certificate can be easily forged. All it contains is a number that needs to be checked against a new database that was created in 2012 for that matter. That's why you need to wait 2 business days after your oath to apply for any citizenship-exclusive service (such as passport), they need to make sure it's updated.
In Australia and NZ, it is possible to endorse your foreign passport with the citizenship mention. While Australia does it electronically (their Immigration online system is outstanding), NZ simply stamps your foreign passport with a special mention, and gave the instruction to all the airlines to accept that stamp as a citizenship proof.
But again, the best way to avoid all the problems is to request a Canadian passport, which has been ranked 2nd in the world as the most trusted passport
In Australia and NZ, it is possible to endorse your foreign passport with the citizenship mention. While Australia does it electronically (their Immigration online system is outstanding), NZ simply stamps your foreign passport with a special mention, and gave the instruction to all the airlines to accept that stamp as a citizenship proof.
But again, the best way to avoid all the problems is to request a Canadian passport, which has been ranked 2nd in the world as the most trusted passport