FFXIII first week sales will outsell Halo 3 first week sales, worldwide.

[Mummelmann]

Hmm, Final Fantasy attach rates are far below Halo, but this is FF's debut on new hardware and it's very anticipated much like FFVII was.
Tough call, but I say no. I do think, however, that FF XIII lifetime sales will pass Halo 3 lifetime with a significant margin.