Neoprene Leggings.

The hydroskins are definitely very stretchy because they're only a half millimeter thick so you should be fine. For winter many canyoneers will wear thicker neoprene wetsuits.

As for restriction and flexibility…surfers wear neoprene all the time and do a lot more than even the most adventurous canyoneer. Neoprene is perfectly fine, you may not like them but consider the cold alternative without ;)

Some of the guys I paddle with wear the NRS hydroskin pants for off-season training when the water is cold.

They fit like a wetsuit or a pair of tights. If you get any of the thin ones (up to say 2 or 3mm thickness) they will be perfectly fine to hike in as far as maneuverability goes.

They might get too warm when not hiking in the creek though.

As an avid Crossfitter with bad knees I wear neoprene compression sleeves on squat days. Regardless of temperatures there is sweat running down my legs from just from the knee sleeves, I can't imagine how full length leggings would be.

I have lots of neoprene experience and use it regularly in 0-20C35-55F degree weather. It works fine. Only one caveat – it is not windproof. And while it keeps you wonderfully warm in water and can keep you too warm on land, when its wet and its windy, the evaporative energy loss will freeze you.

Derrick