Former Ontario Police Officer. Advice will become less relevant as the time goes by !
There is no form for them to fill out, so when you go to the early resolution meeting you can advise the prosecutor that you have a witness that will testify on your behalf.
Since the video itself does not show you actually littering but only walking away, the person shooting the video would need to testify.
If the prosecutor will not drop the charge then you ask for disclosure and a trial date. For disclosure you need to ask for officers notes, witness statements and copy of video.
+++ This is not legal advice, only my opinion +++