The common thread with legal aid, as a government program--which the federal government does contribute to, by the way, even though it's within provincial jurisdiction for the most part--and the court challenges program is that they both facilitate access to justice. So in that sense, they are common.
But the court challenges program is focused on test cases. It's focused on developing the law on issues that have not been before the courts, whereas legal aid is your everyday case--it's ensuring that the law is meaningful to individuals.