The only difference in brakes listed anywhere I can find is the Australian GT86 GT, which has 277mmx24mm discs up front and 286mmx10mm discs in the back. The Australian GTS has the same brakes as the FRS and BRZ.
If somehow the base BRZ here comes with the smaller brakes it should be pretty obvious since they're about an inch smaller in diameter. If you want a solid answer call a parts guy and ask for part numbers for both models.
If you do that, also check to see if that's something new after a certain build date since I've seen no indication by aftermarket companies that there's a difference up to this point.
http://www.ft86club.com/forums/showthread.php?t=21267