If suction mount, then with an additional leash for the camera to the handle, with snap ring/carabiner. Finding a flat part of deck sometimes brings it so much closer to the paddler, while one sometimes wants more distance. though.
One can fix a stabdard gopro-mount onto a rod and tie that rod with velcro onto the handle (e.g. industrial velcro from tesa, super strong)
However, you can also take the upper half of the standard gopro handlemount and use two zip ties, put them like an eight around it. Means you'll need 8 of them if you rent the boat 4 times lol ... and small nail scissors.
Removable, see bike handlebar mounts on google:
Axia alloys gopro mount
rammount gopro handlebar
M-B1R gopro mount
Skygrand handlebar
Kingtide gopro mount
some need that 90°gopro connection piece inbetween and I'd allways use a leash, too.
I use an ISY ITT 500 on my epic handle (it's similar to a gorillapod)... I just wrap the arms around the V7 handle, cam additionally secured to the handle with its own leash though, ball mount would move in tough surf/waves though. For my Hawx I have it fixed on the black rudder cover (got a second cover and perma-fixed the mount onto it).