I had worked in a large company, though in a very entry level. There was a great deal of bureaucracy and politics. Management was very adamant about keeping confidential information safe and securely disposing of it when necessary. Despite my attempts, including asking various people, no one defined for me what was considered confidential information. For example, I was given a task to clean out a desk full of paper and wasn’t sure what was considered confidential and had to put it all in the (overflowing) secure disposal bin. Can companies do this? Make you sign agreements not to disclose any confidential information (either during or after employment with them) but never define what they consider confidential?
I cannot speak specifically for Canada but in Australia "breach of confidence" is a tort at common law so unless there is a Canadian (Federal or Provincial) statute it is probably the same.
For breach of confidence to be established the following elements must be established:
The information must be secret or confidential - it must not be public knowledge. It must also be identified with precision and not just in general terms. A company cannot say "Every document we give you is confidential" - that is not precise enough.
It must be given in circumstances where the recipient knew or should have known that it was confidential.
It must be an unauthorised use to the detriment of the person communicating it.
Effectively, this is the definition of confidential information.
Even if these elements are proved there are defences available:
Public interest - of particular relevance to governments but is generally applicable. For example, disclosing that a corporation was breaching environmental law is not a breach of confidence
General iniquity - where it would be unjust to treat the disclosure as a breach of confidence.
If you sign a non-disclosure agreement then as well as the tort, disclosure may be a breach of contract - what the contract actually says is relevant here. It may define confidential information in a different way than the tort does, usually by removing the third element, however, it would still need to be clear or the NDA would be void for uncertainty.