Sports that require the co-ordinated movement of the upper and lower body will naturally activate your abs/core muscles. Sports in which this rotational movement is constant will give the abs/core muscles an intense workout.
Some obvious examples I can think of (I'm sure there's more):
Kayaking (As you mentioned):
The abdominal rotation and the paddling motion will activate the abs/core muscles. The obliques will be hit hard when trying to control your balance against a heavy current or when making sharp turns.
Mid-flight maneuvers E.G. Spiking & blocking a volleyball, dynamically activates the abs/core. During a spiking maneuver, the upper body will tense and rotate sharply to transfer power to the shoulders and arms.
It is important to contract the abs/core muscles to have a streamlined posture when aiming to glide through the water.
A strong core will act as the base from which to rotate for each stroke.
Exercises like the handstand etc. will work the abs/core when trying to maintain good balance and posture. I imagine this is the case for most gymnastic exercises.
The rings exercise comes to mind as something of an extremely intense abs/core workout.
Lastly, I would like to point out that there is plenty of weight exercises which indirectly work the abs/core.
E.G. Overhead press (requires you to brace your core to prevent your back arching), Renegade row (basically an advanced plank) etc etc.