Originally Posted by
relangford
When my wife got her US citizenship (OK, it was 40+ years ago), she had to verbally (and maybe (??) in some kind of a document) renounce any and all previous citizenships to the US official. Is this not still the case? However, I don't think she ever told the other country. If not the case today, does she still retain, even now, her previous citizenship?
I also agree this would be the smoothest. You are lucky that you are going to HK before China since the airline would want to see your Chinese visa in your passport before allowing you on the plane if going directly to China.
Different countries have different rules. Chance are that the other gov't does not recognize that the citizenship has been renounce if not done in front of their own consular officer and/or the appropriate form has been filled out.
If OP was returning to US directly from China, OP would just present both passports at check-in and let the airline decide what they need to do to comply with both Chinese and US procedures. Passenger responsibility is having the correct documentation/visa etc. Filing that information with gov't authorities is with the airline. For the US procedures, I would imagine the airline would capture the US passport information to fulfill APIS requirements. At exit immigration, Canadian passport will be presented.