That isn't possible. The timing from when Stop Opponent Ability would activate and when Vansaar's ability would activate wouldn't allow Stop Opponent Ability to effect Vansaar, or any other Leader.
I wonder what happens if there are 2 of 2 kinds in your hand?
All are cancelled. 2 or more leaders, same or different, in one player's hand => all leaders of that player have their abilities nullified. (Already two of anysort trigger the "Cancel Leader" Bonus which -surprise, surprise- cannot be cancelled and is in fact the only thing that can cancel Leader abilities.)