What is the test for using a sniffer dog in a search?

R v. Kang‑Brown and R v. A.M. involved the use of sniffer dogs in the context of a bus station and school search respectively. The principles from these cases were applied to a to a traffic stop in R v. Yeh, at para. 47: I appreciate, of course, that the facts in this appeal are somewhat different than those in Kang‑Brown. Most significantly, [the Accused] was detained by the police on a traffic stop prior to the dog search and the facts which are said to have justified the search came to the attention of the police by virtue of his detention. However, in my view, this distinction is ultimately of no legal significance. There is no reason in principle why facts which come to light as a result of a lawful traffic stop should be excluded from consideration when the police determine if they have a reasonable suspicion of a possible drug crime so as to warrant a sniff search.

Comments about the reasonable suspicion standard and the use of sniffer dogs in R. v. Kang-Brown and R. v. A.M. are generally applicable to the use of sniffer dogs in traffic stops. Writing for the majority, Binnie J. held in R v. Kang‑Brown, at para. 25, that sniffer dog accuracy underlies the reasonable suspicion standard: The charter standard of “reasonable suspicion” is based, as stated on the minimal intrusiveness, narrowly targeted objective and high accuracy of “sniffs” by specifically trained dogs […]