I apologize if this has been posted before, but I couldn't find it on search.
I was in HMV today and I saw a flyer (I'll scan it in later, my scanners not working at the mo). Basically if you register your HMV card at www.hmv.co.uk/wii you get to pre-order your wii before everyone else. It won't guarantee you a wii, but it'll certainly give you a headstart.
I'm not sure if they are running this in Canada, but for any canadians out there it's worth poping into HMV to check.