Une partie peut contre-interroger un témoin autre que l'accusé sur toute circonstance tendant à démontrer un biais, un intérêt ou de la corruption

R. v. Megill, 2021 ONCA 253

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[109]   The motive of a witness to testify is a subject that may be explored in cross-examination. For example, a witness may be cross-examined about circumstances that tend to show bias, interest or corruption. The witness' denials may be contradicted by evidence as an exception to the collateral facts rule: see, for example, Attorney General v. Hitchcock (1847), 1 Ex. 91; McDonald v. The Queen, 1959 CanLII 25 (SCC), [1960] S.C.R. 186, at p. 191; and R. v. S. (A.) (2002), 2002 CanLII 44934 (ON CA), 165 C.C.C. (3d) 426 (Ont. C.A.), at para. 32.

[110]   In general terms, a party who intends to impeach a witness called by an opposite party must give the witness an opportunity, while the witness is in the witness box, to provide any explanation the witness may have for the contradictory evidence. This rule, the rule in Browne v. Dunn as it has come to be known, reflects a confrontation principle in the context of cross-examination of a witness for a party opposed in interest on disputed factual issues: R. v. Quansah, 2015 ONCA 237, 323 C.C.C. (3d) 191, at para. 76, leave to appeal refused, [2016] S.C.C.A. No. 203.

[111]   The rule in Browne v. Dunn is rooted in considerations of fairness:

i.      to the witness whose credibility is attacked, by alerting the witness to the intended impeachment and offering the witness the opportunity of explanation;

ii.      to the party whose witness is impeached, by providing notice, thus the opportunity to decide about introducing confirmatory evidence; and

iii.     to the trier of fact, by ensuring that it is not deprived of the full picture of the impeachment and its response, thus not compromising the accuracy of its verdict.

See Quansah, at para. 77.