I'm not sure why you want to use silicone (I assume you mean a silicone-based caulk?). Are you worried about different expansion of the metal vs wood? Silicone will accommodate that, but will provide a somewhat rubbery bond that might be a bit unsettling to people going up the stairs unless there is a tight fit between the wood and metal. But if that is the case, there won't be room for different expansion anyway!
I think I would also favor an epoxy.