Legal advise courtroom?

I reside in Ontario. Canada We recently had a case conference and now it is set for trial. The witness the defendant is bringing in has a severe criminal record. Eight counts of sexual assault. Being the plantiff could I not ban him in from coming. The defendant hadn't used her witness at the case conference and never told the courts until she felt her case was week. and now we move on to a trial. Yet again another $100.00. If the defendant losses could I add that to my costs?