How long are you planning to stay in China? If it is over 6 months, you can definitely state your residential address is the one in China. You could use your address in Canada, too - you will be considered a Canadian resident for tax purposes. But the only benefit of stating your residence is in Canada is that you then won't have to prove you will go back to Canada. But when the visa officer is assessing the application 14 months from now (or whenever), and sees that you have been in China the whole time, but claiming your residence is Canada, they will most likely ask for proof you are going back to Canada anyhow.
You can use the fact that you are on a family-visiting visa as part of the proof you will go back to Canada.
I would use the address you are actually living at as your residential address, never mind what type of visa you have. You can always attach a letter to that section of the forms, explaining your situation in more detail: you could state that your permanent residence is ___ in Canada, but that you have been on a family-visiting visa since ____ in China and staying with your wife, so you put your residential address as the one in China.
Definitely put that you are living with your spouse. For one thing, you have a short relationship, so any proof you have that you are cohabiting should be emphasized. Any time that you two have stayed together should be mentioned on the forms, even if it was just a short visit.
Many forum members have spent 6 months or longer in Canada as a 'visitor', but have used their sponosr's address as their residential address. They have reported no problems with doing this. If you use your wife's address as your residential address, you will be doing the same thing, just in reverse.
If you do decide to use your Canadian address as your residential address, make sure you make it very clear to the visa officer that you are actually in China living with your wife.
