To determine with certainty whether it is made of copper, or brass, make a tiny nick on it, and see whether the color is pink-ish or yellow.
It seems to lack a "rolled lip"... which both a canteen spout and a scabbard-throat would have.
Also, in the photo, it LOOKS like the bottom edge is not a straight cut, but instead wavers, like somebody did a crude job of cutting it.
In the photo, your crushed circular (or oval) tube is about 2.25-inches long. If it was crushed completely flat, it would be a bit longer, about 2-&-3/8th-inches or perhaps 2-&-1/2-inches. If I recall correctly, there is a mathematical formula for determining the original diameter of a circle which has been crushed flat. But I can't remember what that formula is. Knowing its original diameter might help in figuring out what it is.