There are two important aspects to Evans J.A.'s formulation of the rules for judicial review of administrative interpretations of law. First, where the statute is clear, there is no room for deference. Ambiguity is the gateway to deference:
This is American-style "Chevron deference". I do not agree with this approach: see e.g. here and here. I fear that the application of the principles of statutory interpretation will lead judges to find "clear" answers on a regular basis even where deference would otherwise be appropriate. Indeed, unreasonableness as a possible standard of review of an administrative interpretation of legislation only arises when the statutory provision in question is ambiguous and “there is no one interpretation which can be said to be ‘right’”: CUPE, Local 963 v. New Brunswick Liquor Corporation, 1979 CanLII 23 (SCC),  2 S.C.R. 227 at 237. Hence, if a reviewing court concludes that one interpretation is “right”, after conducting a textual, contextual, and purposive interpretative analysis of the legislation, and giving careful and respectful consideration to the tribunal’s reasons, correctness is the standard of review. In these circumstances, if a tribunal has interpreted the statute in some other way, the court may intervene to ensure administrative compliance with the legislature’s clearly expressed intention. The rule of law requires nothing less.
After all, the purpose of the principles of statutory interpretation is to help judges to find the best answers to legal questions. They are not designed to identify ambiguity; they are designed to resolve it. Having found the best answer after applying the principles of statutory interpretation, judges are likely to insist that the statute is clear and no deference is due.
In the United States, the inquiry into whether a statute is "clear" is generally (the point is not free from controversy) superficial and does not involve the full application of the principles of statutory interpretation. If Chevron is to be imported, then its modest approach to determining clarity should also pass border control.
Second, if the statute is ambiguous, there is another question. Did the decision-maker have the authority to interpret the statute?
This looks like what the Americans call Chevron Step Zero. Before deference can be given to a decision-maker, the court must establish that the decision-maker has been delegated the authority to issue binding interpretations of law (see e.g. the comments of Breyer J. here). However, not all those entrusted with the exercise of statutory power necessarily have the delegated power to decide questions of law, including the interpretation of their enabling statute. Of course, from time to time all statutory delegates may have to form an opinion on whether the law permits them to take some particular administrative action, including enacting subordinate legislation. But this is not the same as a statutory power to decide definitively the meaning of a provision in an enabling statute, subject only to judicial review on the presumptive standard of reasonableness. Whether the delegated statutory powers of any given public official or body include the power to decide question of law, including the interpretation of their enabling legislation, may be determined by reference to [a series of] factors... These factors include the terms of the delegate’s statutory mandate, the delegate’s relationship with other decision-makers in the statutory scheme, practicality, capacity, and procedure.
In my view the principles of statutory interpretation should only be admitted, if at all, on this question: whether the decision-maker had authority to interpret the statute. A court saying "I have applied the principles of statutory interpretation and it is clear that the best answer is that X has the authority to interpret the statute" is much less likely to undermine deference to administrative decision-makers than a court saying "I have applied the principles of statutory interpretation and the statute is clear, so no deference is due".
Even here, I am ambivalent. Isn't the "decision" whether a statute is the decision-maker's home statute or a closely connected statute entitled to deference, at least presumptively? Would Evans J.A.'s approach replace this inquiry? Which is more likely to produce deferential reviewing courts? But this question is not settled in Canadian law and Evans J.A. provides a plausible framework for addressing it.
I accept that if we are to have the principles of statutory interpretation anywhere, it would be better to have them here, at Chevron Step Zero. But I do not think we should admit them all. "Mr. Chevron, please go to interview room number 2 and await interrogation by an immigration officer".