I bought a dual can holder from Adventure Trailers to put on my Eezi-Awn roof rack. Yes, they're expensive, but I wouldn't dismiss it on that alone. Of the ones I looked at, it seemed (to me) to have the best system for securing/capturing the cans. Some of the dual can holders don't have a divider between the two, and I was concerned that would result in some movement if I decided to only load one can.
A couple thoughts/disclosures:
I've got to mount it horizontally (roof rack), and some of them don't look like they're intended to be mounted that way. If you're mounting it vertically, that CBI holder would be worth a look.
I didn't run across that MetalTech holder, but it looks really similar to the AT holder.
As far as the differences between the scepter fuel and water cans, the cans appear to be the same size, but I haven't measured them. The lids definitely have different profiles.
I've got a scepter fuel and water can sitting in it in the garage; if you'd like, I can snap a quick picture if that's helpful.