The Ryanair size limit for free bags is 40x25x20 cm (= 15.7"x9.8"x7.8"), aka. 20 liters.
The Kanken measures 38x27x13 cm (15"x10.6"x5") aka. 16 liters, vs. the Rangeland measures 16"x12"x7" aka 21 liters.
I guess it depends on your budget. The Kanken is a bit of a classic design and they're supposed to be very durable, but it's fairly basic in terms of features, doesn't max out the volume allowed, and the straps aren't the most comfortable. It's also more than twice the cost of the Rangeland. The Rangeland looks like good value and many reviewers comment it's comfortable. On the other hand, some people comment the zippers broke in a short period of time.
If it were me, I think I'd be too skeptical of the durability of the Rangeland. If your budget stretches to it, the Osprey Daylite 6+6 suggested by u/Narrow-Tour1071 is probably a great choice. A budget option with better durability is the Decathlon Quechua NH500 backpack for $39, which measures 15.7x11x7.9 - pretty much exactly the Ryanair requirement. It comes with a 10 year warranty. I have the 32 liter version and it's really comfortable, and it's holding up well so far.
I've used this one. I have the one with the long zipper, not the one with the front pouch. It has internal straps, a padded laptop sleeve, and most importantly, side compression straps. You can cinch your load down and make sure you aren't going to have bulges that can make the bag harder to fit in the sizer. It's a little more expensive than rhe folding bags (which I've tried), but it's more durable and much more comfortable to carry.