Are both monitors connected to the same pc, so that one shows the left side, and the other the right ?
If not, and each monitor is connected to its own pc, then it's easy.
If yes, it's fairly easy. Just create a new window within Excel, find the relevant sheet in each windown, and adjust the size and position of each window manually so that one is on the left and the other on the right.
If your monitors are in some other configuration, please give more details.
OK so it sounds as if both screens would display the same thing, yes ?
In which case, I don't think this is really an Excel problem, it's more about the settings on your pc, and getting it to send two different signals, one to each screen. I don't know if this is do-able, it might be, try messing with your computer's settings.