I was actually thinking about this today while mowing my yard (helps the time go a bit faster).
Anyhow, I simply think the BIlls are going to follow the example of the Baltimore Ravens in the Play-offs last year--they resigned Bryant McKinney to a new deal today. If you recall, at some point towards the end of the year, the Ravens decided they were going to start their 5 best lineman, regardless of the listed position. I think that is what the Bills are about to do as well.
Several posters have suggested that Zanders, maybe even Hairston or Pears might move inside. I think it could very well happen; that is, if they are among the top 5 linemen on the team.
I, however, think that Brown played pretty well when called upon last year, and I would not be surprised at all if he does end up being the starting LG.