Another note from Canada on the issues of collateral evidence. This one comes from an appeal court on the East Coast.
R. v. Ryan 2011, NFLD Court of Appeal:
33 A trial judge has a discretion to admit rebuttal evidence provided that the Crown demonstrates that it did not know of the evidence or could not have anticipated the need to call it during its case in chief, and provided that it relates to an issue which arose in the defence. (R. v. Krause,  2 S.C.R. 466; R. v. Aalders,  2 S.C.R. 482; and R. v. Lawes,  3 S.C.R. 694). These threshold criteria address trial fairness, in that an accused is entitled to know the case against him so as to fully answer it and defend himself. This fundamental right would be meaningless if the Crown were permitted to split its case so as to have the advantage of the last word. On the other hand, if an accused adduces evidence of which the Crown was unaware or for which the Crown did not reasonably foresee the need, the rules of fair play governing the search for truth at trial dictate that the Crown ought to have the opportunity to reply to it. Both the accused and the Crown must have the opportunity to hear and respond to the submissions of the other. (R. v. Krause,  2 S.C.R 466, at paragraph 16). If the Crown meets the threshold criteria, then the court must address other admissibility considerations. It is at this stage that the collateral evidence rule could operate to prevent proposed rebuttal evidence from being admitted.
34 An early expression of the rule against rebuttal on collateral matters is found in A.G. v. Hitchcock (1847), 154 E.R. 38 (Ex. Ch.). Hitchcock says that evidence which connects to an issue before the court is not collateral. The case also suggests that evidence which depends for its relevance entirely on the fact that it contradicts the testimony of a witness, is collateral. In practice, the rule against collateral evidence stipulates that answers given by a witness to questions put to him or her on cross-examination concerning collateral matters are treated as final and cannot be contradicted by extrinsic evidence (A. Byrant, S. Lederman, and M. Fuerst, The Law of Evidence in Canada, 3d ed. (Markham: LexisNexis, 2009)).
35 The reason for the collateral evidence rule is to avoid unduly prolonging litigation by proving and disproving facts which do not really matter to the substance of the litigation. In other words, the collateral evidence rule is a rule of trial efficiency.
36 The interplay between the rebuttal evidence rule and the collateral evidence rule was addressed by the Supreme Court of Canada in Krause. In Krause, McIntyre J. referenced collateral evidence in setting out the general rule relating to admissibility of rebuttal evidence at page 474:
The plaintiff or the Crown may be allowed to call evidence in rebuttal after completion of the defence case, where the defence has raised some new matter or defence which the Crown has had no opportunity to deal with and which the Crown or the plaintiff could not reasonably have anticipated. But rebuttal will not be permitted regarding matters which merely confirm or reinforce earlier evidence adduced in the Crown's case which could have been brought before the defence was made. It will be permitted only when it is necessary to insure that at the end of the day each party will have had an equal opportunity to hear and respond to the full submissions of the other.
... Where something new emerges in cross-examination, which is new in the sense that the Crown had no chance to deal with it in its case-in-chief (i.e., there was no reason for the Crown to anticipate that the matter would arise), and where the matter is concerned with the merits of the case (i.e. it concerns an issue essential for the determination of the case) then the Crown may be allowed to call evidence in rebuttal. Where, however, the new matter is collateral, that is, not determinative of an issue arising in the pleadings or indictment or not relevant to matters which must be proved for the determination of the case, no rebuttal will be allowed.
37 A few years later, in R. v. Aalders,  2 S.C.R. 482 Cory J. spoke about collateral evidence in describing the test for admissibility of rebuttal evidence at page 498:
In my view, the crucial question with regard to the admission of rebuttal evidence is not whether the evidence which the Crown seeks to adduce is determinative of an essential issue, but rather whether it is related to an essential issue which may be determinative of the case. If the reply evidence goes to an essential element of the case and the Crown could not have foreseen that such evidence would be necessary, then it is generally admissible. Thus, if a statement is made during the course of a witness's testimony at trial which conflicts with other evidence relating to an essential issue in the case, reply evidence will be permitted to resolve the conflict.
38 Justice Cory went on to distinguish collateral evidence from evidence going to an integral element of that case at page 500:
The reason for permitting evidence to be led in reply in this case is not simply that the reply will affect the credibility of Aalders for all testimony in a case will, to some extent, be subject to testing for its credibility. Rather, it is the fact that the evidence goes to an integral element of the case coupled with the recognition that the Crown could not have foreseen the accused would testify in this way which makes the evidence admissible in reply. ...
39 Three years later in R. v. Lawes,  3 S.C.R. 694, the Supreme Court considered whether rebuttal evidence was relevant to an alibi defence or whether it was merely going to the accused's general credibility, in which case it would be collateral. In endorsing the decision of the Alberta Court of Appeal to admit the rebuttal evidence, Cory J. described how the impugned evidence was relevant at paragraph 2:The rebuttal evidence introduced by the Crown relating to O.H. was properly admitted. It went to the context and the essential fabric of the alibi defence ... The rebuttal evidence was clearly relevant to an issue raised in the defence.
40 Questioning on collateral matters, especially during cross-examination, is often helpful to triers of fact who must decide the credibility of witnesses and the reliability of their evidence. Few would dispute that questioning a witness about his or her previously told lies is admissible for the purpose of helping the court determine whether to believe the witness this time, or that context evidence given in the narration of a witness' testimony may be collateral, but nevertheless admissible because it facilitates the court's understanding of that witness' evidence. As well, several common law exceptions to the strict rule have developed over time in order to permit the receipt of collateral evidence when circumstances dictate.
41 In addition to requiring that the threshold criteria be met, the law limits the calling of rebuttal evidence by stipulating that it cannot be collateral; it must relate to a main issue in the case. Proposed rebuttal evidence relating to the general credibility of an accused or a witness is not sufficient to justify admission. If the proposed rebuttal evidence is relevant to a main issue, then the collateral evidence rule should not prevent its admissibility for such rebuttal evidence can assist the trier of fact in determining the main issue. If it relates to a main issue it is not collateral. This does not mean that all proposed rebuttal evidence that is not collateral must be admitted. Even if admissible, a trial judge may decide not to admit rebuttal evidence if the time, effort and expense involved in its admission would unduly delay the trial or involve the parties in proving and disproving matters of marginal importance. There are degrees of relevance. The more important the proposed evidence can be to a main issue in a case, the more likely a trial judge will exercise his or her discretion in favour of admissibility even if it takes time. It depends.