Has your opencv build support for gstreamer ?
If no, rebuild opencv with gstreamer support.
If yes, it may be that opencv3.2 had not yet backend argument in API, so try rather removing cv2.CAP_GSTREAMER. 0 is the 4CC code, but isn’t used for gstreamer backend, so 0 should be ok.
Also, note that with python the identation is important for branch blocks such as if, while, etc… If camera cannot open, I would expect it to abort and exit, so not see next error messages. Be sure to reproduce code with same spacing.
Resizing with opencv is possible, but would be done with CPU, it would be slow for high resolution.
Why would one prefer a slow solution with CPU usage while there is a HW block that can do that very fast with almost no CPU overhead ?