You definitely should fight careless driving. Careless Driving is one of the most serious offences you can be charged with under the HTA. You're looking at 6 demerit points, a possible licence suspension, up to $2000 in fines (I know the total payable is $490 but I wouldn't just pay it), and your insurance company is likely to either terminate your coverage or virtually double your rates if you get convicted!
File for a trial. Hwy 2 - was this in Scarborough?
You should be able to plea-bargain it down to Red Light - Fail to Stop. At least that's $325 total payable, and 3 demerit points with no licence suspension. MUCH better than careless. Your rates would likely be affected but not as much as if you had Careless Driving on your record. Fill out a Notice of Intent to Appear (available at the courthouse, or in some cases, on line) and take the ticket with it to the courthouse to file. You'll eventually receive a Notice of Trial. Then you can file for disclosure (we'll explain later). Since the officer did not witness the collision, they'll need other witnesses to attend the trial. With disclosure, the Prosecutor will (read: should) disclose all of the relevant evidence against you, including the officer's notes, collision report, and possibly witness statements.
I'd still suggest seeking out a paralegal for this charge. It's pretty serious and a committed legal representative is probably your best bet at this point.
Hope this helps.
* 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