Some canteens were aluminum, although most were stainless. I always sought out the stainless variety, since the water seemed fresher when coming from the stainless one.
The more important part, was the cup, which we used for everything.. heating shaving/washing water, cooking up C-rations, and scooping some coffee from the 10 gallon pot of coffee, brewing in the mess tent, when in the field..
It was of course accompanied by the SS mess kit..