We use a reasonable prospect of conviction and that the prosecution serves the public interest. There are variations, slight variations, between jurisdictions, but all of the prosecuting authorities across the country do the two-step model: is there enough admissible evidence to meet a threshold, and would a conviction be in the public interest? British Columbia does have a different standard. As well, all of them have a public interest component.
On March 10th, 2016. See this statement in context.