Does my son need to get a visa from his fathers home town to stay in China, or Can I travel to HK to geta visa

My son was born in China, and has never left, he has recently received his Canadian citizenship papers, (as I am Canadian he was Canadian at birth), and will soon receive a Canadian passport, this means he will need a visa to live in China, can I take his passport to HOng Kong to get these papers or does his father have to go to his hometown to get these papers? AND, does my son need a letter of permission to leave the country, even though he is no longer a Chinese citizen? because this is what I was told by the consulate, but this seems strange to me.
You see China does not recognize dual citizenship.

he has dual-citizenship now, if he has canadian citizenship. he shouldn't have any problems living in china if he was born there.

well... sum ting is wong is hong kong so i suggest not.