This is another myth that probably began from some jurisdiction in the United States, but in Ontario this is not required. I believe this holds true in all other Canadian jurisdictions as well. This applies for both Radar and Laser units, which are the two types of speed measuring devices in common use by police services in Ontario.
Speeding is considered an absolute liability offence, which means that the Crown does not have to prove that you intended or even knew that you were speeding. They only have to prove that you were. An absolute liability offence means that there are no defences of due diligence available to the defendant to excuse their actions. The key piece of evidence the Crown needs to prove the offence of speeding is the measurement from the speed measuring device. The officer’s verbal evidence in court as to what reading he locked on the device will be sufficient evidence to prove the speed (though not necessarily the whole case). The officer’s verbal evidence can be challenged but if all you do is disagree with the speed they testify to, it is not likely you will be believed, unless the officer has credibility issues. The court usually weighs officer’s accounts of numbers heavily, since they were specifically in the execution of their duties at the time and made notes of everything during the incident or shortly thereafter.
With respect to not being allowed to view the device, Section 46 (2) of the Provincial Offences Act entitles defendants to “make full answer and defence.” However, creating a proper defence for a speeding trial does not require that the defendant viewed the speed measuring device to confirm that the officer read it correctly. Reading the numbers on a digital display is one of those things that police are trusted to be able to do accurately so claiming that the officer read the numbers wrong will probably not be the key to creating a proper defence. It would be up to the defendant to articulate why they feel the officer was wrong in their particular case and how their inability to confirm the reading prejudiced their ability to make a proper defence. To my knowledge no one in Ontario has successfully made this argument yet, but if you’d like to be the first, give it a shot!
Personally, I rarely ever showed people the Radar or Laser I used, except maybe if it was a confused old grandma who didn’t speak English very well and clearly had no idea what was going on. First, because it’s just not relevant to a person’s ability to make a defence, since I was confident in my ability to read the digital display properly and second because I know an officer who showed a roadside device to someone to check the reading and had the person grab it from them and smash it on the ground! In my experiences the bosses are not very happy when you cost the service more than twice as much as it would have cost them to pay you to stay home for the day…ask me how I know! :)