They have an epoxy coating with on the inside which contains BPA or BPA substitutes like BPB. Tetrapaks have a polyethylene liner and polyethylene and typically doesn’t have plasticizers added.
Tetrapaks are laminated, meaning that various layers of solid materials are glued together. Think of it as a sticker on something.
For cans, the epoxy is a liquid coating that's applied by spraying or roller coating, more like paint.
Polyethylene, in addition to being a safer molecule, uses catalysts which don't end up in the final product, which means you can't be exposed to them.