In the Course, go to the Settings page and then Feature Options menu. Click the first radio button for ePub export from left to right to see the ON/green checkbox symbol. Repeat this step for all courses where you’d like to download as ePub.
In the main Canvas navigation (brown menu bar on the left) click Account Icon with your picture, then Settings menu
Find the ‘Download Course Content’ button on the far right of the screen and click it. Select the course and ‘generate ePub’ to start the process. You will receive an email when it is ready.
Canvas Documentation on ePub files