This feature is a less well-known or well-publicized "hack." To use it, simply go to your course home page [1] and type "/undelete" at the end of URL (web address), then click your enter or return key on your keyboard.

You will see a list of content items you have deleted from your course since the course was created. Simply click the "Restore" button to restore it.

From Canvas Support:

“The undelete page is not a supported page in any manner, it is for internal (Instructure Support) use. However, word was spread about the resource, so we don't do anything to prevent users from accessing the undelete page and utilizing it. The page only holds a limited amount of items at a time and won't necessarily restore everything it "allows" you to restore, etc.

Undelete page doesn't display all deleted items, and only a small amount of each type of item on the page.

There really isn't a designated sort order for the page and doesn't have any display or customization.

It only lists a limited amount of items on the page. If you restore items, it will give room to display more of the deleted items. Aka - you delete 20 items, you might only be able to see 10/20 of them on the page, but restoring a few will start giving you access to the other 10/20.