Replacing a 5m section of toerail for that seems excessive. Maybe it can be bent back into shape with some clamping and/or a good few thwacks with a hammer (and a piece of wood to protect the anodizing)? Did you take the stanchion foot out yet? The gelcoat definitely needs repairing under there, it's probably leaking now.
It's not recommended to add larger backing plates to stanchions, as that just means a larger hole in the deck when they get ripped out.