Here's how tell for sure. everyone says blue enamel bottle are all ww1 and it was changed to green in ww2, mainly yes. But, the RCAF kept using identical blue bottles, only difference being, there is a small ring attached to the neck or shoulder of the bottle where the cork chord is attached. In ww1, there were no rings and the chord/string was sewn directly onto the wool cover. you will feel the ring under the wool if its there.
Now, being a ww1 collecting and liking rustic items the most, I have to ask if you still have this canteen and if you would consider selling it?