I travel a lot. Not between Canada and USA. But other countries and USA and I cross other borders. I carried my receipts for a while. But no one has ever bothered me concerning LV. It makes cautious sense but if you were really trying to smuggle stuff in you could find a way to get a receipt to cya. I almost think it makes you look more suspicious that you can produce a receipt. Majority of people aren't that cautious. Hopefully if your items are being used (not still in boxes) you will just be left alone.
Regrettably if you run into a shady customs agent (which I did once) common sense really doesn't come into play. When they start grabbing your items and talking sternly to you as if you are a criminal. You are really at their mercy.
In that situation, I didn't understand the language so I couldn't argue. My interpreter tried. I had to pay duty to bring the item into their country. Only cash. You know where that money ended up.