-Consular processing must take place at a US consulate located at the applicant's country of birth or last foreign residence.So, if you have Canada green card, you can use a US consulate in Canada for consular processing. Otherwise, you need to do it in China.
如果轉回中國,我的通信地址應填中國的吧。
-You can use your address in Canada for communication and you just need to go to China for the interview.