If we don't have free will and all of a persons actions/thoughts etc is directly a reaction on something that happened in the past it will logically be possible with 100% accuracy to predict the future if you had all the information about what happened in the past.
But, since the universe is infinite in all directions, in all dimensions, the information about things happened in the past will also be infinite. Every time an atom moves a little there will already have happened an infinite number of things. In that little bit it moved it would have passed an infinite number of points in space. And every time it moved it would interact with everything else in the universe in an infinite number of ways, at least that's what I believe.
It's like throwing a dice, it will have infinite points on which to bounce off, so it could move in an infinite number of ways after it bounced off.
So do we have free will? I think we somehow have, but only limited free will.
My conclusion is that if an definite number of actions happened in the past(i.e. the universe wouldn't be infinite) we would not have free will.
But I can't really argue that we have complete free will if an infinite number of things happened.
Of course there's always the possibility that the universe is shaped like a banana and not really infinite, who knows?