As I see it, there are two major differences between Google and Facebook and CSIS.
First, and most important, those are private companies and they do not carry out the powers of the Canadian state or any other state, nor do they have police powers.
Second, you say that everyone agrees to provide their personal information to Facebook or Google. But not everyone does. I agree with you that most Canadians, maybe even a large majority of Canadians, choose to do so, but it remains a choice.
However, when an individual’s personal information ends up in CSIS’ database, it is not the result of a choice. Moreover, people choosing not to provide their personal information to CSIS are exactly the ones whose personal information you would most like to see in that database.
Think about police states. As a lawyer practising in the field of refugee rights, I can tell you that China, North Korea, Iran and countries that repress rights and freedoms use the information we are talking about here in a non-transparent, uncontrolled way, which makes those freedoms fictional and nonexistent. By that, I do not mean that Canada is acting in that way, but we are actually talking about protecting ourselves against it.