Here's the deal with Best Buy, at least till the end of the holidays. (This is only in reference to the US. Not sure what BB Canada's policy is)
Wii's - will only be sold in store when advertised. A lot of Best Buy stores don't have Wiis right now period. They are being horded somewhere else. So, when stores say they don't have any, a lot of times that really is true.
Anyway, there will definitely be Wii's for sale next week, so the 17th is pretty much a sure thing since it will be in conjunction with the new weekly ad. Also, because of the ad policy, don't expect Best Buys to just put out shipments when they get them. Sure, I suppose a few stores might violate policy and do so, but really just keep an eye on the paper and ads to know exactly when BB is going to sell them.
PS3s are a different story though, especially due to the limited and very random supply. PS3s go out on the floor right after they come in. If any of you are PS3 hunting too, one last shipment of PS3s is probably but not garanteed before X-mas. And, expect that shipment to be fairly small.