…Justice is not only about results, it is about how those results are obtained.
Justice Abella, R. v. Babos,  1 S.C.R. 309 at para. 85
Plea bargaining veers into impropriety when a Crown Attorney attempts to bully or intimidate an accused with threats of additional charges if they exercise their right to a trial. Justice Moldaver, speaking for a majority of the Supreme Court of Canada in R.v. Babos,  1 S.C.R. 309, provides helpful guidance as to the limits of proper negotiation, beginning at para. 59:
… It is perfectly proper for the Crown to indicate that it will drop certain charges, grounded in the evidence, if the accused pleads guilty. It is also proper for a Crown to advise counsel that if evidence arises at the preliminary inquiry that would support additional charges, they may be added to the indictment under s. 574(1)(b) of the Criminal Code. Where discussions of this sort occur with counsel after substantial disclosure has been provided, the accused and his or her lawyer are able to make an informed decision as to how to proceed and nothing improper has occurred.
The Crown's conduct in this case was of a different nature. The impugned comments were made early on in the proceedings, before the appellants and their counsel had sufficient disclosure to make an informed decision as to how they wished to proceed. Moreover, in at least one instance, the comments occurred in the presence of one of the appellants, Mr. Piccirilli. And the Crown's language was nothing short of threatening. Mr. Piccirilli was told, for example, that if he did not settle, he was going to be [TRANSLATION] "hit by a train". Put simply, the Crown's threats were intended to pressure the appellants into foregoing their right to a trial.
Without question, the bullying tactic to which Ms. Tremblay resorted was reprehensible and unworthy of the dignity of her office. It should not be repeated by her or any other Crown. In her capacity as a Crown, Ms. Tremblay's role was that of a quasi-judicial officer. Her function was to be "assistant to the Court in the furtherance of justice, and not to act as counsel for any particular person or party" (Boucher v. The Queen,  S.C.R. 16 at p. 25). In threatening to charge Mr. Piccirilli with more offences if he did not plead guilty, Ms. Tremblay betrayed her role as a Crown. Manifestly it is the type of conduct the court should dissociate itself from.