The exercise of prosecutorial discretion is not subject to routine judicial oversight.
The deference accorded to the exercise of prosecutorial discretion finds its roots in the independent functions of the prosecution and the judiciary and the practical difficulties with regular judicial review. As Moldaver, J. discusses in Anderson, 2014 SCC 41, beginning at para. 46:
The many decisions that Crown prosecutors are called upon to make in the exercise of their prosecutorial discretion must not be subjected to routine second-guessing by the courts. … Judicial non-interference with prosecutorial discretion has been referred to as a "matter of principle based on the doctrine of separation of powers as well as a matter of policy founded on the efficiency of the system of criminal justice" which also recognizes that prosecutorial discretion is "especially ill-suited to judicial review": Power, at p. 623. In Krieger, the Court discussed the separation of powers doctrine as a basis for judicial deference to prosecutorial discretion:
In our theory of government, it is the sovereign who holds the power to prosecute his or her subjects. A decision of the Attorney General, or of his or her agents, within the authority delegated to him or her by the sovereign is not subject to interference by other arms of government. An exercise of prosecutorial discretion will, therefore, be treated with deference by the courts and by other members of the executive ... . [para. 45]
The Court also noted the more practical problems associated with regular review of prosecutorial discretion:
The quasi-judicial function of the Attorney General cannot be subjected to interference from parties who are not as competent to consider the various factors involved in making a decision to prosecute. To subject such decisions to political interference, or to judicial supervision, could erode the integrity of our system of prosecution.
While prosecutorial discretion is accorded deference, it is not immune from judicial oversight and is reviewable for well-founded allegations of abuse of process (Anderson at para. 48).
Justice Moldaver provides the following useful conceptual framework for the judicial review of Crown decision-making in Anderson beginning at para. 35:
There are two distinct avenues for judicial review of Crown decision making. The analysis will differ depending on which of the following is at issue: (1) exercises of prosecutorial discretion; or (2) tactics and conduct before the court.
All Crown decision making is reviewable for abuse of process. However, as I will explain, exercises of prosecutorial discretion are only reviewable for abuse of process. In contrast, tactics and conduct before the court are subject to a wider range of review. The court may exercise its inherent jurisdiction to control its own processes even in the absence of abuse of process. [Emphasis in original].