A large number of Canadian institutions have started to produce OERs. Some of them are listed below.
In Manitoba, Manitoba Open Textbook Initiative has partnered with BC Campus to access the large amount of Canadian authored OER textbooks and supplementary material they host. eCampusOntario's Open Library has a similar interface that searches the same material, but with some additional Ontario content.
In addition to titles specifically labeled "OER", there are hundreds of Open Access Book Publishers that may have monographs on relevant subjects. A curated list is available at our Scholarly Communications and Open Access LibGuide.
As well, many OERs live in institutional repositories, and can be found by using search engines such as CORE.