Although Canada doesn’t have a constitutional “case or controversy” rule, in practice the courts have discretion to refuse to answer references if they conclude that the questions posed are too general or there is insufficient evidence to allow a decision to be made. See the Reference re Goods and Services Tax for an example - the Supreme Court declined to answer one of the questions on these grounds.
As well, because a reference is such a high profile matter, they tend to be used only for very serious questions, where a legal point, normally of a constitutional nature, is definitely in dispute, and there are parties on both sides of the issue. Reference re Firearms Act (Canada) is a good example, where the federal government and some of the provinces had very defined positions and a clear difference of opinion over the constitutional issue.
Another point is that because the reference can be asked in advance, it can be used in cases where it might be difficult just to wait for a regular court case to come up. The best example of that was the Patriation Reference, [1981] 1 S.C.R. 753 [no online cite that I can find] which was actually three separate references. Prime Minister Trudeau had announced that the federal Parliament would pass a resolution implementing fundamental constitutional chages, with or without provincial consent. Three provinces (Newfoundland, Quebec and Manitoba) responded by referring the patriation issue to their provincial courts of appeal, with subsequent appeals to the Supreme Court of Canada. That approach enabled the provinces to require the federal government to justify, in law, its proposed course of action before it went ahead and tried to make fundamental constiutional changes on its own initiative. Ultimately, the decision of the SCC forced a compromise on all the parties.
If the courts could only rule after the fact, once an amendment had passed by the British Parliament in response to the federal request, it could not have been reviewed by the courts. What would that have done to the political legitimacy of the new constitutional provisions, such as the Canadian Charter of Rights and Freedoms?
A similar example of the reference process being used to get guidance in advance was the Reference re Secession of Quebec. There were all sorts of uncertainties about the constitutional issues raised by the possiblity of Quebec secession. Which is better: to try and resolve those uncertainties in advance, so everyone knows the ground rules, or to have to deal with them on the fly, during a post-referendum period, without much chance of getting a judicial ruling in time?
Overall, it’s arguable that the reference procedure has increased the accountability of the government, by ensuring there is a way to get judicial review of matters that ordinarily would not get into court in time. For example, because of the difficulties of “undoing” a constitutional amendment, I understand that the U.S.S.C. has stated that the validity of constitutional amendments are a political matter, not a judicial matter. In Canada, the power to get advance rulings from the courts on such issues means that is not the case here, at least to the extent indicated by the Patriation Reference and Reference re Secession of Quebec.