Criminal - Appeals - Miscarriage of Justice [s.686(1)(a)(iii)]. R. v. Coristine
In R. v. Coristine (Ont CA, 2023) the Court of Appeal considers the test for miscarriage of justice, here focussing on issues of credibility:
 A miscarriage of justice occurs where “a trial judge is mistaken as to the substance of material parts of the evidence and those errors play an essential part in the reasoning process resulting in a conviction”: R. v. Morrissey (1995), 1995 CanLII 3498 (ON CA), 22 O.R. (3d) 514 (C.A.), at p. 541. This is a stringent standard. The misapprehension must be about a substantial portion of the evidence and not a detail, and it must be material rather than peripheral to the trial judge’s reasoning process: R. v. Lohrer, 2004 SCC 80,  3 S.C.R. 732, at para. 2.. R. v. Kahsai
 Where the misapprehended evidence is used to assess credibility, the issue of whether there has been a miscarriage of justice turns on the extent to which the misapprehended evidence played a role in the trial judge’s credibility assessment. If the trial judge mischaracterized parts of the appellant’s evidence that were central to the trial judge’s assessment of her credibility, it is more likely that the appellate court will find a miscarriage of justice: R. v. Alboukhari, 2013 ONCA 581, 310 O.A.C. 305, at paras. 36-38; R. v. S.R., 2022 ONCA 192, at para. 15.
In R. v. Kahsai (SCC, 2023) the Supreme Court of Canada considered a 'miscarriage of justice' appeal ground, here where the criminal court appointed amicus curiae to an unrepresented defendant:
 The issue to be decided is whether a miscarriage of justice arose. Mr. Kahsai does not claim to have suffered actual unfairness, but contends that the delayed and limited appointment of amicus led to an appearance of unfairness that rises to the level of a miscarriage of justice under s. 686(1)(a)(iii) of the Criminal Code.The court applies these principles in paras 73-77.
 To succeed on this appeal, Mr. Kahsai must show that the amicus appointment in his trial created an irregularity so severe that it rendered the trial unfair in fact or in appearance (R. v. Khan, 2001 SCC 86,  3 S.C.R. 823, at paras. 69 and 73). He will establish a miscarriage of justice if the gravity of the irregularity would create such a serious appearance of unfairness it would shake the public confidence in the administration of justice (R. v. Davey, 2012 SCC 75,  3 S.C.R. 828, at para. 51, citing R. v. Wolkins, 2005 NSCA 2, 229 N.S.R. (2d) 222, at para. 89). This analysis is conducted from the perspective of a reasonable and objective person, having regard for the circumstances of the trial (Khan, at para. 73). It must also acknowledge that while the accused is entitled to a fair trial, they are not entitled to a perfect trial, and “it is inevitable that minor irregularities will occur from time to time” (Khan, at para. 72).
 The “miscarriage of justice” standard — already a high bar — is even higher when claimed based on perceived unfairness instead of actual prejudice. When the perceived unfairness of a trial is at issue, “the appearance of unfairness must be pronounced, such that it would be a serious interference with the administration of justice and offend the community’s sense of fair play and decency” (Davey, at para. 74). Whether a miscarriage of justice arose is a question of law reviewable for correctness (R. v. Schmaltz, 2015 ABCA 4, 599 A.R. 76, at para. 13, citing Schmidt v. The King, 1945 CanLII 4 (SCC),  S.C.R. 438, at p. 439).
 Courts have found a miscarriage of justice based on perceived unfairness in a range of circumstances, including where defence counsel shared confidential information with the trial judge, in breach of solicitor-client privilege (R. v. Olusoga, 2019 ONCA 565, 377 C.C.C. (3d) 143); where the trial judge showed prejudgment by implying that a defence witness was committing perjury in his testimony (R. v. Sherry (1995), 1995 CanLII 1027 (ON CA), 26 O.R. (3d) 782 (C.A.)); where defence counsel did not prepare the accused to testify (R. v. Simpson, 2018 NSCA 25, 419 C.R.R. (2d) 174); and where the accused was forced to proceed without representation, despite their stated wishes and being faultless for their circumstance (R. v. Al-Enzi, 2014 ONCA 569, 121 O.R. (3d) 583; R. v. Pastuch, 2022 SKCA 109, 419 C.C.C. (3d) 447). As these examples show, the appearance of unfairness must be serious enough to taint the administration of justice to rise to the level of a miscarriage of justice.