Halifax (Regional Municipality) v. Canada (Public Works and Government Services, 2012 SCC 29, released a few moments ago, has a good summary of the law regarding the standard of reasonableness review:
 Reasonableness review is concerned both with the transparency and intelligibility of the reasons given for a decision and with the outcome of the decision-making process: Dunsmuir v. New Brunswick, 2008 SCC 9,  1 S.C.R. 190, at para. 47; Montreal Port Authority, at para. 38. As Abella J. has recently explained in Newfoundland and Labrador Nurses' Union v. Newfoundland and Labrador (Treasury Board), 2011 SCC 62,  3 S.C.R. 708, "the reasons must be read together with the outcome and serve the purpose of showing whether the result falls within a range of possible outcomes": para. 14.