Careless driving? You'll need to find out exactly what that "independent witness" saw. When you get a trial date, you can file for disclosure and get the officer's notes, as well as the collision report. That should tell you what this witness supposedly saw.
I'd still recommend getting some sort of professional help with this particular charge. It's very serious.
FYI - if you disobeyed a traffic signal, even if you were going straight, you are 100% at fault (Ontario Fault Determination Rules) for insurance purposes. However, if you were not able to stop in time for the amber light, and you were otherwise driving a reasonable and proper speed for the conditions, then that would not be disobeying a traffic signal. There's also a difference between "fault" and the Highway Traffic Act. Police do not use the Fault Determinaton Rules to decide who to give a ticket to - or at all. They charge based on the HTA. It is possible to be charged by police in a collision, but be 0% at fault according to the Fault Determination Rules. They're two separate pieces of legislation.
Just out of curiosity, what was the speed limit on that road?
* The above is NOT legal advice. By acting on anything I have said, you assume responsibility for any outcome and consequences. *
http://www.OntarioTicket.com OR http://www.OHTA.ca