What GPU do you have?
If your GPU setup is capable of running 3 screens right now you will be able to span 3 screens by going to the Nvidia panel>set up multiple display>span displays with surround. Make sure your 3 monitors have the same resolution to do this.
Also 3 way SLI titan is overkill. Like butchery, Those cards are $1000 a pop one would suffice for anything really, but maybe 2 would be ok. Can't see any reason to drop $3000 on them!