Fair use is an exemption to U.S. copyright law that allows the use of copyrighted works without permission or payment of fees in order to encourage teaching, learning, creativity, and scholarship. It is the most flexible exemption in copyright law, but that also means that it is the most ambiguous. As a result, it has become the most litigated copyright exemption in the U.S. The majority of the time, the courts side with educational uses of fair use; however, that does not mean it is a free-for-all pass. It is important to understand a few conditions surrounding copyright before you make an evaluation.
First, you should consider whether the item you want to use has a realistic alternative that is either free from copyright restrictions (in the public domain) or has a license attached to it that allows for your use. Examples of such licenses are open licenses, such as Creative Commons licenses, that are free of most copyright restrictions, or library-licensed e-resources, such as an e-textbooks, which could allow for multiple users to access and download the content during the semester.
These pages will help you find potential alternatives to the copyrighted work. Keep in mind that these alternatives don't have to completely replace the resource you have planned to use in your course (e.g., a textbook). You can always incorporate reasonable portions* of the work in addition to alternatives to build a collection of resources to use in your course that students do not have to purchase.
If you feel confident that there is no realistic alternative to use in your course in the public domain, with an open license, or licensed through the library, then you can make a fair use evaluation for including the copyright work in your online closed classroom (Canvas).
*Note: "Reasonable portions" is not a defined amount. A portion should be the portion you need to complete your objective without affecting the market of the original copyrighted work (i.e., not merely duplicating the original work and its purpose). In some lawsuits, such as the fair use case involving the biography of President Ford, a small portion was used, but it was considered to be the "heart of the work" and thus affected or harmed the market for the original work (i.e., people read the portion published in TIME magazine about Ford's pardon of Nixon, and thus, it was determined that there were fewer sales of the book).