I'm always confused between canal and channel after I see that different teachers refer to the same thing with two different variants: canal and channel. Are indeed both (canal and channel) used for the same thing in the correct English?
While channel and canal have the same origin, and have meanings in the same area, in ordinary English, they are quite separate, and it would be rare for them to be interchangeable.
Channel is a general word for a place where water or other fluids can pass: it is also used metaphorically, as in channel of communication.
Canal, apart from some specialised medical uses, only means an articial waterway originally built for boats or ships. We wouldn't normally use the word for an irrigation trench, for example.