My sword form feels rusty and it’s been awhile since I attended a sword form seminar, but I’ll take a stab (sadly, pun intended) at answering your questions. I may be completely wrong, so I too would appreciate corrections and comments from others.
For Pushing the Canoe with the Current:
After Dusting in the Wind (3) there’s a transitional step to get you to the corner, I think holding the sword in place is a general ward here.
Then, as you swing the sword back, down, and flip it up again, that general move (that we see elsewhere too) is for slicing your opponent’s wrist on their sword arm. I think the slice can be either on the down-swing or the up-swing. The up-swing can also be to flick their sword out of their hands, iirc, but I’ve never seen it done.
Then, you lift the sword, and allow the point to fall/tilt (in a controlled way, of course) to 45 degrees without pushing forward yet. I think this is a preparatory position but I don’t know if it has a particular application. The weight is still in the back. As you shift forward and extend the right arm, I believe you are pushing your opponent away, kind of heaving them away with the upper third of your sword blade. The left arm protects you. I think of standing in chest high water and pushing a canoe (I’m not in the canoe, but I don’t have any idea if this is the image or not.) Or maybe one is rowing the canoe, but using a pushing-forward stroke like in kayaking. Can anyone clarify the name?
Move 36: Heavenly Steed Flies Over the Waterfall:
I think this one is a whip-slice-jab (dang it, words are hard) to pierce or cut the opponent’s thigh near the knee with the upper third/point of the blade. The power is generated both from the large up-to-down movement where the sword comes from behind the body, over the head, and down (gravity) AND (as always) from the waist turning at the end AND the downward whip- flick of the wrist that’s similar to the sideways whip-like motion of the wrist in #5 Swallow Skims the Water.
I believe Heavenly Steed Flies Over the Waterfall move is designed to attack the legs, but if your opponent gets in the way earlier, I don’t see why it couldn’t be changed into a hack to the shoulder notch, or a gut-puncturing move. Yikes, talking about sword applications is messy!