I'm O/S at the moment, and don't have Regs handy, but we used to carry spare JetA1 in plastic jerrycans quite legally, and relatively often.
I never found a metal jerrycan that had the correct approval stamp in Australia, only plastic ones: RACV in Melbourne sell them, and many of the discount car parts places. If it doesn't have the UN approval stamp, it's not legal
Most metal cans in Australia these days are Chinese copies, and are not suitable for aviation use
The number of cans allowed is listed in the IATA DG Manual, max of 20lt per can, obviously securely strap them down in the cabin or the cargo section, and must be in a cargo area if being carried along with passengers. If a charter/pax flight, they are only allowed if covered in the Company Ops Manual and Company DG manual, and iaw those manuals.