You'll probably need to have them set to the same resolution (your gfx card may well do this automatically).
Have a google on bf4 multimonitor setup....
You'll need the gfx (and cpu) horsepower to go along with this. Unless you have a very high end sli/crossfire setup then you'll be unlikely to run this on anything but the lowest settings.
Google is your friend here (lots of multi monitor info out there)