I am canadian. what do I need to apply a multi entry china visa to stay there over 3 months.

You may just apply for a single entry visa for this trip. Ask your freind to provide you an invitation letter enclosed with your full name, gender, date of birth, purpose of visit, date of arriving and leaving China, place of visit, relations between you, financial support during stay in China her name, contact number, address and signature. Then you may be granted with a duration of 3 months. Or if you were give less than 3 months duration on the visa, you may still apply for an extension of 30 days stay twice when you are in China.