In Saskatchewan (Energy and Resources) v Areva Resources Canada Inc, 2013 SKCA 79 (which I have already blogged about here), the Ministry did not offer any interpretation of the provision at the time it made its decision. After a judicial review application had been commenced, the Ministry duly filed a supporting affidavit explaining its position.
Cameron J.A. was happy to have regard to the affidavit:
And Ottenbreit J.A. relied on it in determining that the decision was reasonable: That being said, after Areva launched its application for judicial review, the Ministry filed an affidavit explaining why in its view the phrase should command the meaning the Ministry had implicitly attributed to it. This is an after-the-fact explanation, and as might be expected the affidavit is largely argumentative in this regard. But that need not detain us, because Dunsmuir makes the point that deference, as respect for the decision-making process, requires “a respectful attention to the reasons offered or which could be offered in support of a decision.” (Dunsmuir at para. 48 quoting from “The Politics of Deference: Judicial Review and Democracy” in M. Taggart, ed., The Province of Administrative Law (1997), 279 at p. 286).
 The Minister’s interpretation of the provision is reasonable because it produces a price and a result consistent with the price and result regarding arm’s length sales as articulated fully and clearly by the Ministry’s rationale for its approach in its affidavit evidence (AB 412a, 437a).Allowing such after-the-fact rationalizations has the potential to cause trouble. That risk is at its greatest where the decision-maker has said nothing at all, leaving judicial-review judges to guess at its thinking and even asking counter-factuals about whether the decision would have been the same had the decision-maker put its mind to a particular point.
Here, however, all parties presumably benefited from having the Ministry's interpretation on the record, all the better to argue about it in court and to plan for future royalty payments.
One could nonetheless imagine the applicant thinking it rather unfair that the Ministry won the case based on an argument it cooked up only after the dispute between the parties had arisen. A particularly angst-ridden applicant would doubtless think that maybe, just maybe, it could have mounted a better argument in its discussions with the Ministry had it only had the full details of the Ministry's position.
Any unfairness here, though, is not the fault of the Saskatchewan Court of Appeal. It is down to the permissive language in paragraph 48 of Dunsmuir which goes far beyond, I think, what Professor Dyzenhaus was suggesting in the essay cited therein.
To ask courts to adopt a permissive approach on judicial review of a fully reasoned decision reached after an adjudicative process is one thing. To allow after-the-fact rationalizations for decisions which might have been reached on entirely different grounds is quite another. It will be interesting to see what the Supreme Court of Canada says about this, if and when they address it.