It would take someone with large gonads to walk up to an adult bear in a predicament like that. Yes, his teeth are in the can, and once the can is off, he will more than likely run off, but his claws are not in the can. One would very likely get seriously hurt trying that rescue attempt bare handed.
I think you could walk a fence post and fence post driver out to the bear, and chain the milk container to the fence post. I think the bear might of been able to remove it himself, if the milk can were fastened to something.
A vet with a dart gun world be the prudent solution. (but I might try the fence post first)