The dissent in R v MacDonald, 2014 SCC 3 (17 January 2014) is so cogently reasoned that one wonders why the majority didn’t refer to it or try to rebut it.
Although I call the judgment of Rothstein, Moldaver and Wagner JJ a dissent, it is really a concurrence in the result and a dissent on an important point of law.
This is one of the annoying things that sometimes crop up in multi-judgment cases: they can look half-baked, as if someone said, “Time’s up, stop writing!” before the majority judges had a chance to say why they disagreed with the minority.
I have always thought that R v Mann, 2004 SCC 52,  3 SCR 59 required reasonable grounds to suspect the existence of facts that made necessary an unwarranted search of a person who had not been arrested. See the heading to my comment on that case on 26 August 2004.
The minority in MacDonald thought that too, as had other Canadian courts in decisions mentioned in their judgment.
Importantly, the minority focus - on the phrase in Mann “...reasonable grounds to believe that his or her safety or that of others is at risk ...” and at  conclude:
“The language of Mann thus appears to stack a probability on top of a possibility — a chance upon a chance. In other words, Mann says a safety search is justified if it is probable that something might happen, not that it is probable that something will happen. As this Court only recently explained, the former is the language of “reasonable suspicion” (R. v. MacKenzie, 2013 SCC 50 (CanLII), 2013 SCC 50, at para. 74). The latter is the language of “reasonable and probable grounds”.”
I mentioned MacKenzie here on 3 October 2013.
Further, the facts of MacDonald plainly show that the officer here did entertain a suspicion, not a belief , and that this was objectively a reasonable suspicion but it would not have amounted to a reasonable belief .
Judicial decisions are not always the best way to develop the law, as the minority note :
“In the end, this case illustrates the danger of leaving police powers to be developed in a piecemeal fashion by the courts. Today, our colleagues impose a standard requiring that an officer have reasonable grounds to believe an individual is armed and dangerous before a “safety search” is authorized, effectively overturning the search power recognized in Mann and a decade of subsequent jurisprudence in the process.”
When I noted Mann, nearly 10 years ago, our legislation required reasonable grounds to believe in the context of a warrantless search for an offensive weapon, but now this has changed to reasonable grounds to suspect: s 27 Search and Surveillance Act 2012. The Act, although in some respects controversial, is at least rational.