It is free-ish. It's free to use but there are restrictive licensing terms that prevent anyone from building anything with it: http://www.canlii.org/en/info/terms.html.
My previous comment was a bit harsh on CanLII. They actually do have an API for building some limited types of applications: http://developer.canlii.org/docs. But certainly not the sort of free and open access that a developer would want for building something like a search engine.
My blog post on this topic: https://www.cameronhuff.com/blog/ontario-case-law-private/ and https://www.cameronhuff.com/blog/canlii-licensing-terms/.