As mentioned above by @Gustavo GeoDrones you can find your Cam URL using https://www.ispyconnect.com/sources.aspx.
Go to the website, click on the model of your camera and a "Cam Video URL Generator" will appear. Insert your IP, username, etc. and click on "generate".
Cam URL for my Canon VB-H45 is (of course with my specific username, password and IP):
http://username:password@IP/-wvhttp-01-/video.cgi
The final code:
cap = cv2.VideoCapture('http://username:password@IP/-wvhttp-01-/video.cgi')