Originally Posted by
eigenvector
I'm not really sure what you gain here by obscuring the countries, but it's possible that you'd need to present valid travel docs for Canada when checking in for the first flight of your return itinerary, even though that flight isn't to Canada. It's normal to check docs for the entire trip at the first point of embarkation to avoid having travellers stranded or denied boarding midway through a trip (and then incurring costs to the airline to return them).
That would be true for a connection. But in the OP's case, there is a stopover. So whatever airline takes him there should be off the hook as far as his return to Canada is concerned.
As far as whether countries check API data to find dual citizenship violators, that's a question that's really beyond the scope of FlyerTalk.
Not more, or less than other document issue. Of course, whether anyone around has the information is a different question. This said, AC ought to be able to tell which countries they pass information to. But again, in the OP's case, it does not look like the airline taking him to country A is AC. Mind you, that airline might well have the information from AC.
There is also the issue of which country would be going to extremes in identifying people with additional citizenships. But eh, bullies are bullies.
. And lately, there even seems to have been cases of attempting to mix up ethnicities with citizenship.