I think 140mm magazines are legal for Carry Optics in USPSA, and the factory mags you reference should be good. I use them there and have never had an issue. I don't know about IDPA and other shooting disciplines.
The Canik 20 round mag is a Canik 18 round mag with a +2 base pad added from the factory.
For shooting USPSA CO, you will *probably* want to change the magazine bases to something like the Taylor Freelance +4 bases. Ideally, their brass ones. The extra weight helps tame a little bit of the recoil and also helps ensure the mag actually drops out of the gun easily when you are doing a mag change in a hurry. "Probably" want to meaning, if you can afford it, you WILL want to.
For those reasons, if you are shopping for Canik magazines, there is no real reason to specifically buy the 20 round mags. If you're going to put a +4 base pad on it, it doesn't matter if you start with an 18 or 20 round Canik mag. Either way, you will end up with, basically, a 22 round mag.
It *might* even be better to start with 18 round mags. I read somewhere (on here, I think) that the spring in the factory 20 round is a little longer, so if you put a +4 base pad on it, it really only gives you +3 ('cause the spring takes up a little extra room). Not sure about that. I have 7 factory mags. 5 of them were OEM 20-round mags and have Wolff Extra Power springs and the TF +4 brass base pads. The other 2 are the 18-rounders that came with my Rival, with the original springs and TF +4 brass base pads. I never put more than 21 rounds in any of them, anyway. A magazine packed absolutely full is just asking for trouble with it either not fully seating when you insert it in the gun, or the slide not going fully into battery when the slide strips that top round off.
Whatever you do, avoid Pro Mag mags for your Rival. They are garbage.
They are workable, but not ideal. They are the 18 round magazine tube and follower, with a longer spring (more coils), different pad, and different pad retainer. The longer pad helps reloads compared to 18 rounders, so they are workable.
But they are not ideal, as they are under the 141mm limit and hold only 20 rounds. You can get 22 rounds with a +4 base pad. Or swap the spring and follower and get 23 rounds (sometimes) with a +4 pad.
That said, if it's all you can get, use them. Mod them with +4 pads or use them as-is to supplement other modded 22- 23-round mags. You don't always need 22 rounds to start, like a speed shoot or classifier standards with a low round count or mandatory reload.