The unanimous outcome (there were concurring judgments from Justice Rowe and from Justices Karakatsanis and Martin) was not surprising - for a few reasons. First, it was an appeal (sought by leave to appeal, and not 'as of right', from a unanimous Court Martial Appeal Court of Canada (CMAC). The CMAC judgment, R v McGregor, 2020 CMAC 8, handed down on the last day of 2020, was a well-articulated judgment. During the hearing before the SCC, the bench gave a distinct impression that they were not swayed by the arguments of either the appellant or the intervener, the Canadian Civil Liberties Association.
What was marginally surprising was that Justice Brown - who was, arguably, the most aggressive in questioning counsel for the appellant - did not participate in the judgment. An observer might reasonably have expected that he would author the judgment on behalf of the court or majority (or plurality). Instead, the judgment for the majority was delivered by the current Court's "Great Dissenter", Justice Côté. And, similarly interesting, Justice Rowe, who perhaps more frequently than any other justice of the SCC, concurs with Justice Côté when she dissents, offered a concurring judgment with a pointed warning to interveners.
Ultimately, the Court held that this was neither the case nor the circumstance to expand upon the lead case on extra-territorial application of the Charter, R v Hape, 2007 SCC 6. Indeed, it is odd that the Court granted leave, only to conclude that "This is not the right case for any reconsideration of the Hape framework." Then again, neither of the parties asked for reconsideration of that framework. Instead, the appellant argued that, within the Hape framework, the Military Judge and CMAC erred. In light of the reasoning offered by the CMAC, the outcome at the SCC was unsurprising.For those inclined to skim through the judgment, the illustrative portions of Justice Côté's judgment may be found at paras 3 and 4 and paras 23 and 24 of her concise reasoning. She concluded at paras 44 and 45:
In sum, the CFNIS demonstrably observed the requirements of the Charter. The investigators discovered the incriminating evidence in the execution of a digital search expressly authorized by a valid warrant. The evidence of sexual assault, although not contemplated in the original warrant, fell squarely within the purview of the plain view doctrine. The CFNIS seized the evidence in accordance with that doctrine and subsequently obtained Canadian warrants before conducting an in‑depth analysis of the files in issue. Even on Cpl. McGregor’s view of the law, it is difficult to see how the CFNIS could have more fully complied with the Charter. In light of my conclusion that the investigative process was consistent with s. 8 of the Charter, it is unnecessary to address Cpl. McGregor’s argument that the evidence should be excluded under s. 24(2). For these reasons, I would dismiss the appeal and affirm Cpl. McGregor’s convictions.
This can be contrasted from circumstances where the Military Police have not been quite so assiduous regarding section 8 of the Charter, such as those experienced in R v Spriggs, 2019 CM 4002, in which Military Police investigators violated a subject's rights under s 9 of the Charter (everyone has the right not to be arbitrarily detained or imprisoned) in order to trigger "search incident to arrest" and thereby improperly bypass the requirement for a judicially authorized search warrant. [Although that matter was terminated for different reasons: abuse of process by Director of Military Prosecutions.]
There was some disagreement by Justices Karakatsanis and Martin regarding whether "plain view doctrine" was relevant in this particular matter (Justice Côté held that it was relevant and justified seizure of relevant evidence; they disagreed that consideration of "plain view doctrine" was necessary). Justices Karakatsanis and Martin spent a considerable portion of their reasoning examining criticisms of the Hape framework and concluded that there remained several shortcomings. However, since the majority of the Court held that this was not the case to re-examine the Hape framework (and neither of the parties were asking the Court to do so), this largely remained academic debate.
The most interesting aspect of Justice Rowe's concurring judgment was his admonishment of interveners (and his implicit disagreement with Justices Karakatsanis and Martin on the scope of argument that interveners may reasonably pursue). This matter had five interveners, of which only one was a provincial Attorney General (Ontario); the other interveners were non-governmental organizations concerned with civil liberties or constitutional rights. Most of the interveners were limited to written submissions, although the Canadian Civil Liberties Association did appear and offer oral argument.
Justice Rowe reminded interveners that: (1) the purpose of an intervention is to “present the court with submissions which are useful and different from the perspective of a non‑party who has a special interest or particular expertise in the subject matter of the appeal” (R v Morgentaler,  1 SCR 462); (2) interveners must not raise new issues or “widen or add to the points in issue”; and, (3) interveners must not adduce further evidence or otherwise supplement the record without leave.
In particular, Justice Rowe reminded interveners that they must be careful to distinguish between developing a permissible legal argument and adding prohibited new issues; the two are conceptually distinct. Consequently, while the judgment does not particularly refine the Hape framework, Justice Rowe certainly offers future interveners a concise roadmap of what is permitted and what they must not do.
Ultimately, this judgment has marginal, if any, impact on the application of military justice. It did not alter the Hape framework. The 'lesson' that, within the Code of Service Discipline, military investigators (whether Military Police or otherwise) must be alive to Charter constraints is a rather obvious lesson. Similarly, where there are likely extra-territorial considerations or issues arising from the conflict of laws, prudent investigators should seek legal advice before taking action (i.e., this is manifestly NOT a circumstance in which "begging forgiveness" is better than "seeking permission"). But that is not an Earth-shattering observation either. Neither was the waiver of diplomatic immunity in support of the investigation surprising. After all, that conditional immunity exists ultimately not for the protection of the individual, but to support the state's interests where that individual is performing duties or functions on behalf of the state.
Even in the broader context of Charter law analysis in Canada, the judgment does not advance greater certainty of the law. It was principally an opportunity for two of the justices to advance academic debate that was not determinative of the judgment.
Perhaps the most notable aspect of the judgment was the debate in the concurring judgments regarding the role and scope of intervener argument before the SCC - and the judgment was not determinative of that issue. Indeed, it was reminiscent of an aspect of the Court's judgment in R v Stillman, 2019 SCC 40 (which very much concerned military justice). One of the issues that was raised in Stillman, to which the intervener 'Advocates for the Rule of Law' dedicated the entirety of their argument, was the extent to which comity and 'horizontal stare decisis' was binding on an appellate court. That issue had not been resolved prior to Stillman. And, in light of the Court's pointed avoidance of the issue in their judgment, it is still not settled law.