Man some days I LOVE Walmart.
Today I went to a Walmart. They had a bunch of 30th stuff. I grabbed a couple of Vipers since I don't have any with the red trim around the arms. Then I look at the price. It's still at $7.92. I took it to a price checker and it says "see an employee". So I go to the checkout, point out the sign and I know they have a rule that says they must sell it for the shown price. Also, they will give you up to $10.00 off your first purchase. So I got 2 Vipers for $7.92 total (plus taxes). So I found my own BOGO free deal and at the old rates. 
Yep, this is something that EVERYONE in Canada should be aware of, its called the Scanner Code of Practise ( SCOPe) and quite a few retailers abide by it. Its not law, but rather an agreed-to policy that many retailers have. The stores that take part show a small sign or sticker at the entrance, and the policy is basically as Morgardee has said: if the scanner and the checkout show a difference, you get the item for FREE (or a discount), up to $10 off.
http://www.competitionbureau.gc.ca/eic/site/cb-bc.nsf/eng/01262.htmlThere's other aspects to this, so reading up on it can be worth one's while.
Bear in mind that not all stores are signatories of this policy, and even some stores within a chain that are signatories may not play along.
If the store is a signatory and you bring it up, the manager might have to go check up on the policy before you can get the discount--which can take some time--and even then then may decline it. Again, it doesn't hurt to ask though....