OP, dress smartly as mentioned, you "can" wear jeans, but you "present" better if your wearing slacks, as PP said go to value village for $6.99 your set. The MOST important thing is make sure everything is clean and wrinkle free, (throw your shirt and slacks in the dryer for 10 minutes, no need to iron.
As for do you have to go. If you have been served a document to attend the hearing then YES you MUST attend. I will respectfully disagree with PP on the possibility of "jail time", (technically it could happen, just as you "can" be charged with speeding for doing 1 km/h over, but you would have greater odds at winning the Lotto Max three weeks in a row..lol) Having said that, the crown, and or the JP, (remember this is traffic court so no judge), may take the position if you can't exert the effort to show up in a case where someone has been charged for hitting you then why the hell should they exert the effort to convict the other driver.
It is also highly unlikely that you failing to attend will have "dire" consequences on your claim for benefits, etc. Your adjuster has many more pressing items n their plate than checking to see if you showed up to testify. The fault is assigned via the FDR, NOT the outcome of the charges against the other driver. Fault, (from the insurer's point of view), was assigned within 24 hours of the claim being opened, they don't wait months for a case to go to court to determine who is or isn't at fault.
Upon arriving, (it is best to show up approx 30 minutes BEFORE the time specified on the court document), present yourself to the police officer, (if you recognize him/her), that did the investigation. If you don't see him/her, then present yourself to the crown and advise that your there. If you provided a written statement, ask if you can see it to refresh your memory of the events. They will let you read it over, take your time, note things such as time/date of collision, what the road conditions were like and was it sunny, dark, raining etc, that day. The copper will also likely speak to you may make small talk, (just to help you relax, I used to do this with witnesses I had at trials). You can then sit and they will go thru all the pleas for the day then begin trials for anyone who is pleading guilty, (or setting dates for future hearings).
The defense attorney, or paralegal representing the other driver may approach you. They may ask questions of what you recall etc. Answer their questions a s best you can BUT keep it brief and to the point, the more you talk the more opportunity you present for them to pick apart your story. Relax, and watch the show. You "may" especially if there is to be more than one witness be asked as the trial begins to exit the court room. If you are sit outside and listen for your name to be called on the intercom. Do NOT discuss details of the case with anyone other than the crown, the police officer involved, and the defense counsel. If someone asks what your there for just state I'm a witness, and leave it at that. If the other driver approaches you, be polite but refrain from ANY conversations beyond that.
It seems daunting but afterwards you will say well that was a breeze. Good luck
