Most Canadians are surprised to discover that we have a secret court, just like the US Foreign Intelligence Surveillance Court, that meets in a bunker in Ottawa, issuing secret warrants to do a range of cloak and dagger activities including wiretapping and installing bugs. But we do. (They are judges designated under the Canadian Security Intelligence Service Act by the Chief Justice of the Federal Court of Canada.)
But one thing that distinguishes Canada from the US in an important way is that designated judges under the CSIS Act have, from time to time, retained "friends of the court" to argue positions in opposition to government requests. It hasn't happened often, but is something that our friends to the south may want to consider as controversy about PRISM and a secret body of evolving caselaw is being established.
Unopposed applications resulting in secret decisions with significant civil rights and constitutional implications easily leads to the presumption that the system is rigged and intelligence agencies get a free ride. While transparency would call for published decisions and open court, independent lawyers arguing the other side is a step in the right direction.
I've managed to find three published decisions from Canada where amici where used, and perhaps there are more that are unpublished.
For example, in Re Canadian Security Intelligence Service Act, 2008 FC 300, an amicus assisted the court in considering whether a jurisdictional issue raised in a warrant application could be heard in public, in open court. (The answer was no, but the decision was published.) In connection with the same matter, in Re Canadian Security Intelligence Service Act, 2008 FC 301, an amicus curiae was appointed to consider whether the court can authorize CSIS to carry out clandestine activities outside of Canada. (The answer was no.)
More recently, in Reference re sections 16 and 21 of the Canadian Security Intelligence Service Act, 2012 FC 1437 (CA), the Court called upon a amicus curiae to help with the question of whether "section 16 of the Canadian Security Intelligence Services Act prohibits the naming of [a Canadian citizen, permanent resident or corporation] in a warrant as [a natural or corporate person] whose communications are proposed to be intercepted, when the warrant is issued in relation to a request for assistance in the collection of information or intelligence from the Minister of National Defence or the Minister of Foreign Affairs relating to the capabilities, intentions or activities of [a foreign state or group of foreign states, corporation or person]." Importantly, the Court agreed with the amicus and denied CSIS the warrant.