How to draw graphics on video Canvas???
On top of the video? In most cases you don't. If the phone supports OverlayControl from the AMMS (JSR-234) then you could use that, but there is no Nokia phone supporting that control yet.
A clumsy workaround is to take snapshots and display the snapshots in succession to generate a "viewfinder". You could then draw on top of these images. This will be slower than the normal video, also you need to make sure that your MIDlet has multimedia recording API access rights set to at least "ask first time", otherwise you are prompted for every snapshot.