Isn't there a difference between declaring passports and citizenships? I would've assumed they would have to include only the valid passport, and then declare having two citizenships. Would what I just mentioned be wrong? and why?
I do not see any specific requirement that you must provide a photocopy of a valid passport
that you do not intend to travel on.
IMM5533 (checklist) says you must provide most recently issued travel document (passport), but does not specify what needs to be done for dual citizens. It then goes on to say that you do not need a valid travel document (passport) at time of applying, but you will need a valid one before travelling to Canada. (Note I looked at outland checklist, not inland, so don't know what it says).
So I'm going to go out on a limb and say that while it's NOT ideal, you can probably submit the photocopy of your expired other passport; might be wise to submit a letter of explanation with it that you do NOT intend to renew it or use it to travel anytime soon and that you will travel on the other passport (all the more so that I think it's a visa waiver country). (Might have more credibility if you have a good reason to not renew, like hard to renew Iraqi passports right now abroad - don't know if that's the case)
But I can't say for certain and have not looked through the full instructions. You really should read through those and check if there are any specific instructions that apply to your case. Obviously I could be wrong and there may be a risk.
(Note - there are other issues that may come up, like you will I assume need to provide most other documents eg birth certificate etc from Iraq if that's the country of birth)