Copyright law protects original, literary, musical, dramatic or artistic works in a variety of forms, including written materials, computer software, and web-based formats.
Copyright protection applies regardless of whether the work in question is published (such as a book or an annual report) or not (such as an internal company memo), and whether someone has made it available to the public (such as on a website) or not. This protection expires 50 years after the death of the originator, regardless of who holds copyright at that time.
A work that is freely available to the public is not necessarily in the public domain.
For a work to be in the public domain, the originator must have specifically waived copyright to the work, or copyright must have legally expired.
Work that is in the public domain can be used by anyone without copyright being violated.
You may be allowed to use copyrighted material in your thesis provided it falls under the Canadian Copyright Act's definition of "fair dealing". Please see Section III of the Canadian Copyright Act for information. If you are in any doubt, you must obtain permission.
In 2004 the Supreme Court of Canada made a significant ruling about copyright and fair dealing in its decision in CCH Canadian Ltd. v. Law Society of Upper Canada. Fair dealing is covered in Section 3: The Law Society and Fair Dealing.
Note: It is good academic practice to cite sources, but such citing does not remove the obligation to obtain formal permission to use copyrighted material that is not covered under "fair dealing".