"Nonrefundable" could mean it can't be cancelled. Technically, you might have to change it for another flight or lose it all. I've had those sorts of tickets. The other thing to watch out for is that if you change it in one direction, the whole booking is subject to change fees. So if you change the original leg the return leg is subject to a change fee, even if it is the same flight because the itinerary was changed. This also happened to me and I was able to avoid it because it was not disclosed.
Some airlines have non-changeable tickets. You don't show up, it's lost. I don't think AC has these.
First sentence above is misleading. "Can't be canceled" sounds like non-changeable. When the next sentence describes non-refundable. Non-refundable simply means that they won't refund. You at best get a credit, minus the change fee. Valid for one year.