Langstaff v. Marson, 2014 ONCA 510:
 There is a strong presumption of judicial impartiality and a heavy burden on a party who seeks to rebut this presumption.
 Judicial impartiality has been called "the key to our judicial process": seeWewaykum Indian Band v. Canada,  2 S.C.R. 259, at p. 288. Chief Justice Lamer referred to "public confidence in the impartiality of the judiciary" as "essential to the effectiveness of the court system": see R. v. Campbell,  3 S.C.R. 3, at para 10. The presumption of impartiality anchors public confidence in the integrity of the administration of justice.
 An allegation of bias engages the very foundation of our judicial system. It calls into question not simply the personal integrity of the judge, but the integrity of the entire administration of justice.
 In order to rebut the presumption of impartiality, a test has been developed by the Supreme Court of Canada. It was first articulated by de Grandpré J. in his dissenting reasons in Committee for Justice and Liberty v. National Energy Board,  1 S.C.R. 369, at p. 394:
[T]he apprehension of bias must be a reasonable one held by reasonable and right minded persons, applying themselves to the question and obtaining thereon the required information. … [T]hat test is "what would an informed person, viewing the matter realistically and practically – and having thought the matter through – conclude. Would he think that it is more likely than not that [the judge], whether consciously or unconsciously, would not decide fairly."
 The Supreme Court has repeatedly endorsed this test. In his reasons in R. v. S. (R. D.),  3 S.C.R. 484, Cory J. explained, at para. 111, that the test set down by de Grandpré J. contains a "two-fold objective element": not only must the person considering the alleged bias be reasonable, but "the apprehension of bias itself must also be reasonable in the circumstances of the case." Cory J. added, at para. 113, that:
[T]he threshold for a finding of real or perceived bias is high. It is a finding that must be carefully considered since it calls into question an element of judicial integrity. Indeed an allegation of reasonable apprehension of bias calls into question not simply the personal integrity of the judge, but the integrity of the entire administration of justice.
 This two-fold objective element is based on reasonableness: the person considering the alleged bias must be reasonable and the apprehension of bias itself must also be reasonable. The reasonable person must be informed and know the relevant circumstances, including the traditions of integrity and impartiality on which the judicial system is based. A mere suspicion is not enough.
 The determination is also fact-specific. In Wewaykum, the Supreme Court held, at para. 77:
[T]his is an inquiry that remains highly fact-specific. In Man O'War Station Ltd. v. Auckland City Council (Judgment No. 1),  3 N.Z.L.R. 577,  UKPC 28, at par. 11, Lord Steyn stated that "This is a corner of the law in which the context, and the particular circumstances, are of supreme importance." As a result, it cannot be addressed through peremptory rules…there are no "textbook" instances. Whether the facts, as established, point to financial or personal interest of the decision-maker; present or past link with a party, counsel or judge; earlier participation or knowledge of the litigation; or expression of views and activities, they must be addressed carefully in light of the entire context. There are no shortcuts.
 This stringent test for a party alleging apprehension of bias is grounded in the need to preserve the integrity of the judicial system. It also recognizes the need to maintain the public confidence in the judicial system. The analysis contemplates a hypothetical observer who is informed of all the facts. It does not depend upon the views or conclusions of the litigant.
 It has also been held that, in order to maintain public confidence in the administration of justice, the appearance of judicial impartiality is as important as the reality. In Metropolitan Properties Co. (F.G.C.) Ltd. v. Lannon,  3 All E.R. 304 (C.A.), at p. 310, Lord Denning M.R. stressed the importance of the appearance of judicial impartiality. He said:
[I]n considering whether there was a real likelihood of bias, the court does not look at the mind of the justice himself.... It does not look to see if there was a real likelihood that he would, or did, in fact favour one side at the expense of the other. The court looks at the impression which would be given to other people. Even if he was as impartial as could be, nevertheless, if right-minded persons would think that, in the circumstances, there was a real likelihood of bias on his part, then he should not sit. And if he does sit, his decision cannot stand.
 This passage was cited with approval by Major J. in his dissenting reasons inS.(R. D.), at para. 11, and by this court in Benedict v. Ontario (2000), 51 O.R. (3d) 147 (C.A.). In Benedict, the court added, at para. 20:
We note that while Lord Denning M.R. spoke in terms of a "real likelihood" rather than a "reasonable apprehension", in National Energy Board de Grandpré J. took care to state that such variations in the expression used should not generally be treated as involving any substantive difference in the approach to be taken. "Reasonable apprehension", "real likelihood", "reasonable likelihood" and "reasonable suspicion" amount to the same standard.
This reasoning accords with the decision of Lord Nolan in R. v. Bow Street Metropolitan Stipendiary Magistrate et al.,  1 All E.R. 577 (H.L.), at p. 592:
[I]n any case where the impartiality of the judge is in question, the appearance of the matter is just as important as the reality.
The appearance of impartiality was emphasized in Weywakum, at para. 66:
[W]here disqualification is argued, the relevant inquiry is not whether there was in fact either conscious or unconscious bias on the part of the judge, but whether a reasonable person properly informed would apprehend that there was.