Why can't they be? You want a fuel bladder: https://www.liquidcontainment.com.au/category/2/Fuel-Bladder...

When I think “Jerry can” I think the very specific rigid 20L vessel. I guess we can call other things a Jerry can too.

I’m curious if these are legally allowed in Canada. If so they seem decent!

"Legality" is going to vary wildly - if you are carrying fuel in the trunk, you're probably pretty restricted, but you may be able to get away with various other mounting options - and I'm sure you can buy them even if you can't run them.

I'd also search out "off road" people and forums, though they may not specialize in your vehicle, they probably know the various rules and regulations.

https://www.zuksoffroadcanada.ca/Gas-Tank-15-Gallon_p_997.ht... does exist, so I'm sure there's things out there. People modifying vehicles for Nunavut or the Australian Outback would be places I'd start.

So do things like : https://masterhitch.com/catalog/truck-suv-accessories/auxili... but I'd be a bit wary of bolting gas tanks to the rear bumper/trailer hitch myself.

And many rules will stop applying once you are "off road" whatever that means in your area.

They sell those! They are used frequently in rescue settings. The can is basically a big cubical heavy plastic bag.

Your alternative is of course to fill some plastic bags from your local grocery store like this [1] lady did.

[1] https://twitter.com/FiendishlyYours/status/13919904872220016...

Holy crap, I don't even have words for that.... just why? It's also quite toxic and she's going to be covered in it now.

I tried that but the fire marshal told me no.