B2L2

FYI:
If you never have a 回鄉卡 before, you will require to get a China passport first, just your HK ID card isn't enough.
If you have a 回鄉卡 before (even expired), you could still renew it without a China passport.

So if you're on the first case, go apply the China Visa with your Canadian passport is the easiest.  If you're going to frequently travel between HK / China and you have 回鄉卡 before, then getting the 回鄉卡 is more convenient.