Basically title, I don't know how to rescale Peggle or anything, and im on a 2560x1440 monitor so im not a fan of windowed Peggle.

There is no way to rescale Peggle unfortunately, so most people play windowed. From what I have tested pixel shots still work in fullscreen.

You can always change your resolution temporarily when playing Peggle. Looks like crap, but at least you don't have to watch a stamp-sized window.