Right, it is a glass jar I am suggesting. Not at all metal cans. It is the "lid" that goes on that glass jar I am suggesting be tin plated steel. Only because today's lids for such purposes are typically tin plated steel, but I don't know enough about glass-jar canning to say lids "have" to be tin-plated steel. If other simpler metals are acceptable by real-life standards, then by all means have the lids be copper or bronze. I suppose cheaper metals would make it stop being the late-game mechanic I am meaning it to be, defeating the whole point of it.
As for the question on whether it's needed or not... Perhaps not. It feels like it's just a nice-to-have thing in the late-game so you don't need to use up animal fat or other somewhat inconvenient to obtain materials for preservation.