I have no experience with pyCuda, but searching the forum for pyCuda on TX2 board you would find some topics such as this one mentioning success although test fails.
I have poor experience with python and have never been able to use opencv cuda libs from python, only CPU side. Other users having had success may share. You may also describe more your use case for better advices.
If you just want to write your own kernel and apply on each frame of video stream, you may try have a look to gstreamer plugin nvivafilter. You can find its sources in public_sources archive that you can download from developer zone (you’d need to be logged in).