Did you even have to ask!
SuperMarioGalaxy will break the million mark within its openning weekend. I can guarantee it their are many factors that benefit Mario's next platforming adventure. First the instilled user base of about 2-3 million gamers who buy every Mario title made. Then you have the new casual gamers who will buy MarioGalaxy because hey "I've always heard of Mario lets try it out". Then its almost Christmas season meaning parents will be out their looking for the next way to spoil their kids.
In other words Mario Galaxy will be the centerpiece of Nintendo's fall lineup. I think the real question should be which game will be the tenth to reach a million. That is more accurate and I will now present my best guesses.
I have three games that I believe are capable of being the tenth game to break the million mark.
#1- The most likely to break the million mark will be Sonic & Mario: At The Olympics. Face it both their combined user bases in addition to the casual friendly mini-game compilation genre. When all is said and done the game looks like it will be a smashing success.
#2. WiiFit is the second runner up despite having a late launch in the year and the fact that it will be launching only in Japan their is a very good chance it will break the million mark within days of being released. Japanese culture isn't like American culture either health plays a very big role. Many companies require employees to excersize before working and their are many more health percautions taken. This makes WiiFit the perfect game to launch in Japan.
#3. MetroidPrime3 the game will have launched in Europe giving it a boost in sales. However Metroid is one of those slower titles and not exactly the fastest game on the charts.
In other words I don't expect any other game to actually beat out Mario:Galaxy for the 9th spot. By the time any of these other titles reach the million mark Mario will already be basking in his glory!