You mean in America, or worldwide?
I'd say it will sell around 600k in America, 200k in Europe and 30k in Japan for a total of 830k first week. Since there's no first week sales data for the previous games in America and Europe, those predictions are a bit random and based on total sales of the previous game :P
This is a hardcore game, therefore a lot of its sales will happen in the first week.
My Mario Kart Wii friend code: 2707-1866-0957