Regardless of the circumstances of the speeding infraction, you wan't to challenge and set a court date! Ideally, you don't even want to defend. Instead, you want to exercise your constitutional rights and have your case STAYED either on lack of disclosure OR delay (sometimes both).
You'll need to do some reading and research on this forum. Also, http://ticketcombat.com is an excellent resource to read up for help.
Step1: Plead not guilty (make sure you check the box that you will challenge the officers's evidence) to set a court date
Step2: File for disclosure (officer's notes, copy of radar manual, etc).
http://ticketcombat.com/step4/disclosurehow.php You have a constitutional right to be tried in a reasonable amount of time. If your court date is 10 months or more from the date of infraction, you can file an 11B Charter challenge.
You also have a right to disclosure. If prosecution does not provide it to you, you can have the case dismissed, or at minimum, the judge will adjourn so prosecution can gather the documents and provide you disclosure. If this is the case, then your court date will be delayed further, increasing your chance of a successful 11B.
In your specific case, the officer may have lost site of you before he pulled you over (given he was travelling the opposite direction on a highway and had to do a u-turn). This strengthens your case in case the disclosure or 11b method do not work and you have to defend yourself. You will get more information about the specific circumstances when you receive your disclosure package (if you get it, lol).
You'll also walk if you officer doesn't show up at court. At worst, you'll plea bargain for a lesser fine and demerit point. So get to the court house and set a court date asap to get the ball rolling.
This is a fantastic forum with valuable information, but you'll have to start your research now and get prepared. Paralegal assistance is also an option.
It is possible and you CAN do it!