Well personally, i still think the Halo brand when it comes to America and on the 360 is bigger than that of Call of Duty. Even though Call of Duty had a huge opener on the 360, Halo is still the brand attached to the Xbox name and most of the fans on the system. It's the equivalent of Mario on the system.
However, 7 million in one month is quite a bit. I never openly state something as impossible unless it's obvious, but this seems like kind of a stretch. Also that it isn't going to be seen as a direct sequel or mainline game, that means it is going to take a much larger and more active marketing campaign. I think MS will definitely have the money injected into it to make it huge, but if it is effective or not will depend on how they do it. That HALO Reach beta though is a good start.
