I don't know what to tell you from a legal standpoint... But I do know that driving with NO plates is better than driving with the wrong plates in this case.
When I bought my first car, the deal was done after business hours, and it was a private sale. I couldn't get the car registered that day, and I still had to do a safety on it. I got my insurance to fax me a temporary card while they mailed my real ones, and obviously had the bill of sale and signed title.
While I was on my way to get a 10-day temp permit from the MTO, I got pulled over. I explained this to the cop, and obviously didn't get a ticket (he would have had to be a huge douche to give a ticket for this). Got my temp tags, then safety and plates, and have had those plates ever since (I was 17 when this happened).
The penalty is in the HTA as follows: [...]on conviction is liable to a fine of not less than $100 and not more than $1,000 or to imprisonment for not more than thirty days, or to both, and in addition the persons licence or permit may be suspended for not more than six months. R.S.O. 1990, c. H.8, s. 12 (1).
Seems like a major ticket, so i'm sure this would have a pretty crappy effect on your insurance rates if convicted.
This is a pretty serious charge from the looks of it.... Your court date on the ticket is usually just a set date. So you have to show up, talk to the crown, etc. Decide whether you're going to be pleading guilty or not guilty, and if you're pleading not guilty they'll set a trial date from that point.
I am pretty sure that since it's probably pretty easy to prove this charge in a courtroom, your best bet is to try to bargain with the crown. If you're young, probably a student, no record, etc. Tell them all this and that something like this can be huge. Tell them that you didn't intend it in a malicious way and that you just weren't thinking, it was stupid, etc.
Depending on your crown and the jurisdiction, they might give you a break. I know in some places they drop 45-over tickets (which is 3 or 4 points and a few hundred bucks) to a "disobey sign" (2 points and 80 bucks), so you might get away with something very minor.
Even a minor ticket will negatively affect your insurance because you're a young male, but often times the insurance company won't check, so they'll never find out. Only major tickets are automatically reported to the insurance. They sometimes check your record on renewal, but it costs them money so they might not.