I use a HP Slate 21.5" to display two pages side by side, and even on a screen that big, I can't view two full-size A4 sheets due to it using a widescreen aspect ratio. It's almost identical to having two 10" tablets side by side in terms of the page sizes. So you would either need to find a 4:3 tablet around 21", or you'd have to find a widescreen tablet that's around 23-24" or larger. The only Android tablet around 24" that I know of is the Nabi Big Tab. I know one user bought this tablet, removed most of the standard stuff on it, and was able to run MobileSheetsPro, so it might be an option worth considering.
Mike
Mike