Awesome canteens Riley! Is that a lead spout on the one?
Not sure if you're looking for any preservation advice, but I would suggest looking into Oxalic Acid. Dump diggers use it to remove rust, while leaving the paint, on old cans.
I've used it a bunch on old cans and also this tin cup from a colonial site.
Its surprised me in the past at whats hiding under the oxidation layer. Just have to be sure its neutralized with baking soda after, but lots of good info online about how to use it.