HKID- whether your baby can get the HKID is subject to conditions case by case. And this is the answer you would get no matter how many times you call or write or personally visit the Immigration in HK. IF your baby was born in HK, then automatically, he is able to get the HKID with 3 stars. However, if he is NOT born in HK, whether he gets one or not will be subject to the approval by the immigration. I can only tell you this: You can try to apply for your baby. However, the factors that will help your baby to get the HKID are:
Proof that you( parent with the HKID) is a permanent resident of HK. LIke you have a job, pay taxes, have property, or rent a place to live,and that you have lived here for 7 years before.... etc. Otherwise, your baby will only be given the HKID after he lives in HK for 7 years.
When you submit the application for your baby, you will be asked a LOT of questions, and will need to submit all the documents and proofs that you are a HK permanent resident, that's why your child needs to have a HKID, to stay here. However, your child's HKID will NOT be 3 star, until he lives in HK for 7 years.
Regarding Canadian passport- Canada recognizes dual citizenship. If any one of you (the parents) are Canadian Citizen, then up until now (they are planning to change the law (debating)... you better hurry.
If one of you is Canadian, then your baby is automatically qualified to get the CDN passport, b/c he is Canadian, no matter where he was born.
You need to submit the application for citizenship card first, which takes 6-9 months, then once you received the citizenship card, you can then apply for the 3 year passport for your baby.
If during this time without the citizenship card, you need to travel with your baby, you need to submit your own passport, and your baby's birth certificate indicating you are the parent, and a proof of air ticket that you need to depart on certain date. They will issue your baby a TEMPORARY passport that is good for 1 year. However, they advised, ensure you really need the 1 year passport before applying for it ,b/c it costs the same as the regular passport, and b/c most countries require you to have 6 months valid on the passport upon entry, you really have only 6 months to use for your baby's temporary passport.
I hope this helps you, and good luck.
P.S. you using the "return home ID" to enter CHINA has NOTHING to do with your baby's stay in China.
Your baby should have the Chinese Birth Certificate when he's born, that means he can stay in China without visa without passport for as long as you want. Upon the exit, you will need a passport to exit, with a exit stamp. If you re-enter, with a Canadian Passport, then your baby would need a visa to re-enter.
I don't know the details about obtaining the Chinese passport for your baby, but remember they do not allow dual citizenship. Many people do not mention they have Canadian Passport when applying for Chinese or HKSAR passport.
Hope this helps you.