From experience and what others have told me, it seems that Canada Customs are more concerned about residents & citzens paying duty rather than bringing in fruits, meats, counterbands (YVR is especially notorious). Believe me, if they see something of potential duty, they will be all over it. I can't recall how many stories I've heard passenger getting busted and fined in YVR for filling out the error amount on their declarations.

On the other hand U.S. customs tend to focus more on fruits, meats, weapons, and counterbands than they are on residents paying duty. On most cases when passengers are selected for secondary inspection, those are the items they are on the lookout for.

Going back to the OP's question, the duty free allowance for residents have been increased from $400 to $800 three years ago as someone has already mentioned.