For a Canadian going into the states there isn't much problem, its taking extra stuff back to Canada where you will tend to get hit.
There are alot of misconceptions, yeah the clerk at the Duty Free Store takes your plate, but it only goes on the sales receipt and is not sent to Customs. I always give a phony plate number because I can never remember my own. Never had a problem. Because of very low duty rates and because of their focus on terrorism, the US border guards will allow a significant amount of alcohol and tobacco in before collecting duty. If its canadian made booze or beer or cigarettes then there is no duty because of NAFTA, only internal revenue tax which is miniscule. They do not collect state sales taxes on the US side of the border. Also they have a minimum amount they have to collect. It used to be $10, where if the duty came to less than $10 they wouldn't collect it because it wasn't worth their time.
Here is the best way to do it:
US Border Guard: What do you have to declare?
You: I bought four cartons of smokes, two bottles of booze and two cases of beer at the duty free store.
US Border Guard: Do you know thats over your exemption?
You: Oh yeah, I have no problem paying the duty.
Us Border Guard: OK no problem, have a nice day.