In Tough As Nails you could refill the canteen at a cauldron, but with this mod you can't.

In another note, if possible, config options for the canteen refill range, capacity and one-click refill as opposed to 3 clicks would be appreciated as well.

Instant refill has finally been added in 0.3.7, better late than never!

Canteens will be refillable with cauldrons in 0.3.0, you can also drink from them
Haven't done the config for instant refill though, will leave this open as I think about it