What must the prosecutor prove to be convicted of a DUI / impaired driving?

 

A: The prosecutor must prove that you:

• were impaired, and
• were operating a vehicle while impaired

Usually, the police use a breathalyzer to test for impaired driving.  The roadside breathalyzer is merely a testing instrument.  The real test admissible in court is given at the police station.  In order to take a breath sample, the police must have a reason to ask you to breathe into the breathalyzer. 

Other issues considered in defending DUI charges is the validity of the testing breathalyzers and whether the police followed the Canadian Charter of Rights and Freedoms properly (right to silence, right to call a lawyer, etc.).

The point is that the prosecutor has a big burden to prove that someone was drunk driving.  There are many defences to impaired driving as well - including Canadian Charter of Rights and Freedoms defences.  As with all guilty verdicts in Canada, the prosecutor must prove all aspects of the case beyond a reasonable doubt.