I don't know your area but the black bears in my neck of the woods can peel off car doors. They would make short work of an ammo can which, unlike a proper bear canister, offers nice edges to give their claws purchase. And if left unattended they will have plenty of time to work on it.
_________________________
If you only travel on sunny days you will never reach your destination.*

* May not apply at certain latitudes in Canada and elsewhere.