whats the difference between the Burstbucker Pro, Burstbucker 2 and the 57 Classic Plus pickups

Not huge, you really have to compare them side-by-side to hear the differences. If you're buying an add-on to upgrade your guitar, don't bother with Gibson pickups - ludicrously overpriced when Bare Knuckles, Fralins etc are of equal or superior quality for less cash.

If you're asking because you want to buy a Gibson guitar, don't base your decision on the pickups it comes with - to my ear a Les Paul sounds like a Les Paul, the different pickups have only subtle differences on the output and tone. And pickups are easy to change if they aren't to your taste - whereas the rest of the guitar, you're stuck with!