So, after some much-needed reading and refreshing my memory, I learned/remembered that crouch-canceling actually has two components that both contribute to its usefulness as a defensive technique. Since this is going to be a conversation about the usefulness of a move (ganon sideB) vs crouch canceling, it's a good idea to go over them thoroughly, just so everyone knows what they're talking about.
a) While you're crouching, you suffer from less hitstun and knockback when attacked. (I've read that it's 2/3 reductions, but I would take that with a grain of salt because I haven't seen the math that backs it up.) If you are hit while crouching, attacks will not send you as far, and you will not be in hitstun for as long. It's just a weird interaction coded into the game, I guess Sakurai thinks crouching should make you not fly as far when you get punched.
...AND
b) If you're holding down on the control stick when you exit the hitlag of an attack, you actually ASDI your character downwards, collide with the ground, and initiate a landing animation.
To explain b) further:
There are two types of hitstun animations. I don't know the official terms for them, but one makes your character just flinch (think of Fox's fthrow at 0%, or any jab) and the other makes your character tumble around and when you hit the ground you'll be able to tech. If the attack had enough knockback (AFTER crouch canceling reduction) to put the opponent into the tumbling hitstun animation, then ASDI into the ground will result in a groundbounce animation which can be teched. If the attack did not have enough knockback to put the opponent into tumble, and it puts them into the flinch animation instead, they will immediately land on the ground once hitlag is over and initiate their normal landing animation. In Captain Falcon's case, this animation is 4 frames long. Then he can take any action he wants, while you're still stuck in your attack animation.
So, when an opponent crouch cancels your attack, there are three possible outcomes:
1) the knockback IS NOT enough to put your opponent into tumble, he ASDIs into the ground, lands normally, and punishes you with whatever he wants.
2) the knockback IS enough to put your opponent into tumble, he ASDIs into the ground, and has a (difficult) tech opportunity. he can miss tech, or tech left/right/ in place normally.
3) the knockback IS enough to put your opponent into tumble, and is also enough to prevent his attempt to ASDI into the ground. he suffers knockback and hitstun and gets sent flying, but not as far as he would have if he didn't crouch. at this point, since it's just knockback reduction and doesn't let you act significantly earlier, it's not really a 'crouch cancel' any more.
Anyways, now that that's out of the way, let's look at some data for sideB vs Falcon.
Bad news...
If you try to sideB from neutral, he can get the best crouch cancel from 0-35%.
He can cc+asdi into the ground for a ground bounce from 36% until 86%. If he's a god, this means he can also tech it.
However, since the original question was about tech-chasing, THIS is the most relevant image. ^^^^
First things first: Even if he holds down during his tech roll, he can't really "crouch cancel", because he can't enter the crouch animation to reduce knockback and hitstun. However, his ASDI will let him ground bounce until 26%. Still works at 25%, so if you start a stock with stomp > sideB techchase he'll be at 22% when the sideB connects and he'll be able to ground bounce, and tech if he's a god.
(My methodology got a little bit weird at this point because I was trying to put Cfalc in a situation where he could be holding down while getting hit, but NOT be crouching. That meant knocking him down first, and the easiest way to do that was with another sideB so I just put his % at 17 below whatever % I was testing. If the opponent is standing and inputs down BEFORE being hit, then he gains the benefits of crouch canceling, and if he inputs down DURING HITLAG, he actually gets an extra frame of SDI and can ground bounce for a couple extra %. The situation that I'm trying to test is one where your opponent is holding down on the stick while being techchased, ie during his missed tech or tech roll animation. Rest assured, thanks to the 20xx hackpack this test results in accurate %s for an unstaled sideB. I redid it like thirty times until I figured out what was going on lol)
I'll come back when I've got numbers for all of top8. In general, I don't really like sideB as much as dair- worse hitstun:knockback ratio for combos (dair is a meteor and thus has 80% knockback against grounded opponents while retaining 100% hitstun), more susceptible to crouch cancel (meteors can't be ASDI'd into the ground). BUT, if you got really good at techchasing with sideB you could make it a really powerful tool since it's Ganondorf's only way to cover 3/4 options at midstage.
...this post ended up being WAY TOO LONG LMAO, I spent more time talking about how crouch cancel works than I spent on actually talking about Orah's question. anyway,the final numbers are
Crouch Cancel normal landing: 0-35%
CC Ground bounce: 36%-86%
ASDI only (tech chase) ground bounce: 0-25%