Not sure why you would need to do this. Generally, the Canadian prices are higher than the US prices. If you do cross the border to buy in a Canadian store, do some research to see if you can get the GST (federal sales tax) refunded. I don't know what the conditions are, but I know that you can get the GST refunded on certain items. It's 5% across the country.
Also, if you are buying something in a smaller store, it is sometimes possible to get the PST (provincial sales tax - different rates per province, sometimes it's 0%) refunded as well. In most provinces, stores don't collect PST on items shipped out of province. Technically, they have to ship the item themselves, but I've known stores to simply write "Shipped to BC" on the invoice and hand me the item. In essence you've become the shipper. Technically, the store isn't supposed to do this... but I've been lucky a few times. You can't just ask them to waive the PST, you should ask them whether they can ship it. Explain that you save the PST. Start figuring out whether the PST is more than the shipping cost. Three times out of ten they don't want the hassle of packing and standing in line at the Post Office, and they just hand you the box.
Luck.
