Copyright laws grant exclusive permission to an author to publish his or her work however he or she sees fit. Any reproduction or derivation of that work, in any form or medium, in part or whole, without his or her express permission is prohibited.
However, notwithstanding this exclusive right, the copyright laws permit an exception, called fair use, that permits copyright protected material to be republished without the author's consent, when such republication is unlikely to diminish the value of the original work and would enrich the literature of the nation. The terms of fair use are deliberately left vague.
According to English Wikipedia:
The Copyright Act of Canada establishes fair dealing in Canada, which allows specific exceptions to copyright protection. In 1985, the Sub-Committee on the Revision of Copyright rejected replacing fair dealing with an open-ended system, and in 1986 the Canadian government agreed that "the present fair dealing provisions should not be replaced by the substantially wider 'fair use' concept". Since then, the Canadian fair dealing exception has broadened. It is now similar in effect to U.S. fair use, even though the frameworks are different.
Magazines Canada (15 September 2009). "Why Canada Should Not Adopt Fair Use: A Joint Submission to the Copyright Consultations" (PDF). Archived from the original (PDF) on 3 April 2016. Retrieved November 16, 2015.
Masnick, Mike (28 May 2015). "Book Publishers Whine To USTR That It's Just Not Fair That Canada Recognizes Fair Dealing For Educational Purposes". Tech Dirt. Retrieved November 16, 2015.
So, the questions you must ask yourself while using those 10 to 30 sentence is:
- Is the non-free work you are copying still protected by the copyright laws in the country of origin? Overseas countries willing to teach English language often use passages from early Sherlock Holmes books, the first two Agatha Christie books, Mill on the Floss, Scarlet Letter and other such works whose copyright protection has expired.
- Does the country of origin have copyright relations with Canada? North Korea doesn't. This question has a lot of relevance in the United States, which has a habit of making new enemies. Canada, as I understand, is engaged in far less international frictions.
- Can you plausibly use free text instead of copyright-protected text?
- Is your work commercial? If yes, how high-profile is it?
- How much of the original work are you using? If it is a short story of 50 sentences, you definitely have a problem. If it is a long novel, assuming the portion you choose is a coherent unit or adjacent sentences, it is okay. If you summarize the whole novel by selecting 30 sentences from its strategic locations, it is not fair use.
- How else would your work impact the original work? For example, using passages from Harry Potter books for arbitrary purposes, when its sale was very strong, would have been far less likely to be approved by a court under a fair-use pretext. But using them in the work of criticism was easily approved at the time.