Crown - Crown Counsel. R. v. Barrett
In R. v. Barrett (Ont CA, 2022) the Court of Appeal comments on the duties of crown counsel:
The duty of the Crown as advocate. Boucher v. The Queen
 Crown counsel, like any other advocate, is entitled to advance its position forcefully and with a degree of rhetorical passion: R. v. John, 2016 ONCA 615, 133 O.R. (3d) 360, at para. 77; R. v. Boudreau, 2012 ONCA 830, at paras. 15-16; and R. v. Mallory, 2007 ONCA 46, 217 C.C.C. (3d) 266, at para. 339.
 However, there are clear limits on Crown counsel. They are not to “engage in inflammatory rhetoric, demeaning commentary or sarcasm, or legally impermissible submissions that effectively undermine a requisite degree of fairness”: Mallory, at para. 340. The Crown must not misstate the facts or the law, invite the jury to engage in speculation, or express personal opinions about either the evidence or the veracity of a witness: Boudreau, at para. 16.
 This is important because “the role of prosecutor excludes any notion of winning or losing; [the] function is a matter of public duty… to be efficiently performed with an ingrained sense of the dignity, the seriousness and the justness of judicial proceedings”: Boucher v. The Queen, 1954 CanLII 3 (SCC),  S.C.R. 16, 20 C.R. 1, per Rand J., at p. 24.
 A trial judge’s failure to provide an adequate jury caution, where Crown counsel’s comments are sufficiently prejudicial, amounts to an error of law: R. v. Clause, 2016 ONCA 859, 133 O.R. (3d) 321, per Brown J.A. at para. 38; R. v. Romeo, 1991 CanLII 113 (SCC),  1 S.C.R. 86, 2 C.R. (4th) 307, at p. 95.
In Boucher v. The Queen (SCC, 1954) the Supreme Court of Canada stated as follows on the role of Crown counsel:
It is the duty of crown counsel to bring before the Court the material witnesses, as explained in Lemay v. The King. In his address he is entitled to examine all the evidence and ask the jury to come to the conclusion that the accused is guilty as charged. In all this he has a duty to assist the jury, but he exceeds that duty when he expresses by inflammatory or vindictive language his own personal opinion that the accused is guilty, or when his remarks tend to leave with the jury an impression that the investigation made by the Crown is such that they should find the accused guilty. In the present case counsel's address infringed both of these rules.. R v Fercan Developments Inc.
In R v Fercan Developments Inc. (Ont CA, 2016) the Court of Appeal comments as follows on the role of Crown counsel:
 When discharging their role, Crown counsel have an obligation to ensure that the power of the state is used only in pursuit of impartial justice: Oniel v. Marks (2001), 2001 CanLII 24091 (ON CA), 141 O.A.C. 201 (C.A.), at para. 67. Crown counsel must discharge their role with the utmost integrity and sound judgment, remaining open to the possibility of the innocence of the accused and avoiding “tunnel vision”: R. v. Delchev, 2015 ONCA 381 (CanLII), 126 O.R. (3d) 267, at paras. 64-65. Though these principles were articulated in the context of criminal prosecutions, they remain relevant in proceedings like this one.. R v Anderson
In R v Anderson (SCC, 2014) the Supreme Court of Canada took the oppourtunity to expound on judicial review available against the Crown with respect to tactics and conduct before the court:
(b) Tactics and Conduct Before the Court
 The second category in the framework for review of Crown activity was referred to in Krieger as “tactics or conduct before the court”: para. 47. As stated in Krieger, “such decisions are governed by the inherent jurisdiction of the court to control its own processes once the Attorney General has elected to enter into that forum” (para. 47).
 Superior courts possess inherent jurisdiction to ensure that the machinery of the court functions in an orderly and effective manner: R. v. Cunningham, 2010 SCC 10 (CanLII),  1 S.C.R. 331, at para. 18; Ontario v. Criminal Lawyers’ Association of Ontario, 2013 SCC 43 (CanLII),  3 S.C.R. 3, at para. 26. Similarly, in order to function as courts of law, statutory courts have implicit powers that derive from the court’s authority to control its own process: Cunningham, at para.18. This jurisdiction includes the power to penalize counsel for ignoring rulings or orders, or for inappropriate behaviour such as tardiness, incivility, abusive cross-examination, improper opening or closing addresses or inappropriate attire. Sanctions may include orders to comply, adjournments, extensions of time, warnings, cost awards, dismissals, and contempt proceedings.
 While deference is not owed to counsel who are behaving inappropriately in the courtroom, our adversarial system does accord a high degree of deference to the tactical decisions of counsel. In other words, while courts may sanction the conduct of the litigants, they should generally refrain from interfering with the conduct of the litigation itself. In R. v. S.G.T., 2010 SCC 20 (CanLII),  1 S.C.R. 688, at paras. 36-37, this Court explained why judges should be very cautious before interfering with tactical decisions:
In an adversarial system of criminal trials, trial judges must, barring exceptional circumstances, defer to the tactical decisions of counsel . . . . [C]ounsel will generally be in a better position to assess the wisdom, in light of their overall trial strategy, of a particular tactical decision than is the trial judge. By contrast, trial judges are expected to be impartial arbiters of the dispute before them; the more a trial judge second-guesses or overrides the decisions of counsel, the greater is the risk that the trial judge will, in either appearance or reality, cease being a neutral arbiter and instead become an advocate for one party. . . . Crown counsel is entitled to have a trial strategy and to modify it as the trial unfolds, provided that the modification does not result in unfairness to the accused: Jolivet, at para. 21. Likewise, as this Court recently held in R. v. Auclair, 2014 SCC 6 (CanLII),  1 S.C.R. 83, a judge may exceptionally override a Crown tactical decision in order to prevent a Charter violation.
The corollary of the preceding is that trial judges should seldom take it upon themselves, let alone be required, to second-guess the tactical decisions of counsel. Of course, trial judges are still required to “make sure that [the trial] remains fair and is conducted in accordance with the relevant laws and the principles of fundamental justice”: Lavallee, Rackel & Heintz v. Canada (Attorney General), 2002 SCC 61 (CanLII),  3 S.C.R. 209, at para. 68.
 Finally, as with all Crown decision making, courtroom tactics or conduct may amount to abuse of process, but abuse of process is not a precondition for judicial intervention as it is for matters of prosecutorial discretion.