Criminal - Disclosure. R. v. Marrone
In R. v. Marrone (Ont CA, 2023) the Court of Appeal reviews the CCC expert evidence disclosure requirements:
(b) The Procedural Context for the Expert Report Issue. R. v. G.B.
 Since the Crown intended to call expert evidence from Det. Lafleur, s. 657.3(3)(b) of the Code required it to deliver, within a reasonable period before trial, a copy of her report, or if no report was prepared, a summary of the opinion anticipated to be given by her and the grounds on which she based it. Although the Code does not specify what the report is required to disclose, a reasonable reading of the provision suggests that it cannot be less than what must be disclosed if there is no report (a summary of the opinion anticipated to be given by the expert, and the grounds on which it is based).
 If the requirements of s. 657.3(3)(b) of the Code are not met, s. 657.3(4) provides that the court, if requested, is to grant specific relief. That relief is an adjournment to allow time to prepare for cross-examination of the expert (although the length of the adjournment is not specified), ordering compliance with the requirement for a report or summary, and ordering witnesses to be recalled to give testimony related to that of the expert witness unless the court considers it inappropriate to do so.
 Sections 657.3(3) and (4) provide:
(3) For the purpose of promoting the fair, orderly and efficient presentation of the testimony of witnesses,
(a) a party who intends to call a person as an expert witness shall, at least thirty days before the commencement of the trial or within any other period fixed by the justice or judge, give notice to the other party or parties of his or her intention to do so, accompanied by
(i) the name of the proposed witness,
(ii) a description of the area of expertise of the proposed witness that is sufficient to permit the other parties to inform themselves about that area of expertise, and
(iii) a statement of the qualifications of the proposed witness as an expert;
(b) in addition to complying with paragraph (a), a prosecutor who intends to call a person as an expert witness shall, within a reasonable period before trial, provide to the other party or parties
(i) a copy of the report, if any, prepared by the proposed witness for the case, and
(ii) if no report is prepared, a summary of the opinion anticipated to be given by the proposed witness and the grounds on which it is based; and
(c) in addition to complying with paragraph (a), an accused, or his or her counsel, who intends to call a person as an expert witness shall, not later than the close of the case for the prosecution, provide to the other party or parties the material referred to in paragraph (b).
(4) If a party calls a person as an expert witness without complying with subsection (3), the court shall, at the request of any other party,
(a) grant an adjournment of the proceedings to the party who requests it to allow him or her to prepare for cross-examination of the expert witness;
(b) order the party who called the expert witness to provide that other party and any other party with the material referred to in paragraph (3)(b); and
(c) order the calling or recalling of any witness for the purpose of giving testimony on matters related to those raised in the expert witness’s testimony, unless the court considers it inappropriate to do so.
In R. v. G.B. (Ont CA, 2023) the Court of Appeal considered a 'stay' as a remedy for alleged disclosure breaches:
 The applicant’s second ground of appeal is that the trial judge erred in dismissing his request for a stay of the charges against him based on what he argued were disclosure failures of the Crown.
 The trial judge found that the Crown’s disclosure had not in every respect been timely and complete − rather, he termed it “sub-optimal”. But he found that prosecutorial misconduct had not been made out, and that the applicant had not been deprived of a fair trial or opportunity to make full answer and defence, because, for example, the late disclosure was still in time for use in cross-examination or was of little probative value.
 A stay is a remedy of last resort, to be granted only in the “clearest of cases” when no other remedy can address the harm: R. v. Babos, 2014 SCC 16,  1 S.C.R. 309, at paras. 30-31 and 36-40. The trial judge’s determination that no such harm was present here and thus to refuse a stay is entitled to deference on appeal: R. v. Graham, 2020 ONCA 692, at para. 18.