I believe 12x16 would be an odd size, at least I don't believe any of the paper's I've used come in that size. i.e. Moab, Epson, Red River... However, they all have 13x19 which would be very close to what you are requesting. I personally prefer to print my images on larger papers leaving a border around the image. Can always trim the border if needed, but the border allows for easier handling and framing.
Roy