are you just changing the rear stock muffler to that ebay cannon or piping to?
if just changing the rear muffler there wouldnt be really any difference going 2 inch or 2 1/4inch...will just be loud and farty, same as having holes in your stock muffler.

if your chaning piping to a 2inch would be recommended, too big and you will loose response and just be loud. if i were you, id stay away from ebay no brands as they will prob sound like crap.