Firstly, "jump cancelling" is a bit of a misnomer. fyi, a "jump cancel" when when you literall cancel your jump by performing a move immediately after jumping, such as a grab or upsmash, so that you dont jump at all, but instead perform the move. So thats that
With the shine platform waveland, you're just jumping out of shine, which is cancelling the shine lol. Anyway, you can do it with any method you choose. Most people just do it with their regular jump button of choice (personally i use X for most jumping, so i use X for my shine platform wavelanding as well)
But its completely up to preference.
However, i'll say that using the X/Y buttons has an advantage of being more convient. Because when you shine, you have to hit Down on the joystick (obviously) using X/Y allows you to simply keep holding down for the waveland. Whereas if you use joystick for the jump, you add a slight level of difficulty because you have to hit down (shine)> up (jump)>down again (waveland) which is a little more tricky for most.
If thats what's comfortable for you tho, go for it. otherwise, keep practicing with X/Y you'll get it.