Sorry, just like to get confirm from you. More stupid questions but do need to know:
4. CBP will record me as canadian citizen? Then dual nationtionalities?
-Based on the Chinese Nationality Law, you have lost your Chinese Nationality because you become a Canadian citizen. So, technically you can not use the Chinese passport anymore. What I commend here needs to follow the law and it is just for your reference.
5. if yes, can I use chinese passport with green card back?
-Up to you, and I have no idea what consequence will be (may be OK or may be not).
