The court has considered two cases where police didn't have much to go on before deploying drug detector dogs on men who were transporting drugs.
The first case concerns Benjamin Cain MacKenzie. In 2006, Mounties in Saskatchewan pulled him over for going 112 km/h in a 110 km/h zone. The officers noted he was sweaty, appeared nervous and had bloodshot eyes, something they said was consistent with having smoked marijuana. They testified it was also significant that MacKenzie was driving from Calgary, a city they said is a well-known source of illegal drugs.
The two Mounties conducted a police check and found nothing on MacKenzie but decided to deploy Levi, the drug detector dog they had with them that day. Levi pointed the constables to the trunk and 14 kilograms of marijuana.
The second case relates to Mandeep Singh Chelil, a man who was pinpointed in 2005 by the RCMP's Jetway Program, which helps police detect travelling drug smugglers.
Chelil exhibited a number of red flags Mounties were looking for, such as travelling alone and buying a one-way ticket with cash. Upon arrival in Halifax on a red-eye flight from Vancouver, the Mounties' sniffer dog Boris pointed out Chelil's suitcase, which contained more than three kilograms of cocaine.
The questions for the Supreme Court of Canada are whether police breached the two men's charter rights to be free from unreasonable search and seizure and if their cases met the "reasonable suspicion" threshold for deploying a sniffer dog.
"Trying to define what reasonable suspicion means is incredibly important because with reasonable suspicion, the officer does not need a warrant to search you and that's the key," said Ottawa University law professor Carissima Mathen.
The way things stand now, Mathen said reasonable suspicion is open to broad interpretation that can lead to arbitrary applications of the law.
"These are the cases where the drugs have been identified. The cases where the innocent person is randomly searched and nothing turns up, they don't get before the courts. So there's that little bit of tension but we can never forget that these cases are likely the minority."
At trial, MacKenzie and Chelil were acquitted. In each case, the judges ruled the police did not have reasonable, objective grounds to search the two men.
And at Chelil's trial, evidence was raised about the dog's reliability. The dog at the Halifax International Airport detected cocaine in Chelil's bag but got it wrong when it pointed to another passenger's luggage that did not contain drugs.
On appeal though, both acquittals were overturned, with the judges disagreeing with the lower courts and finding the Mounties did have reasonable suspicion to deploy the dogs.