In Course Navigation, click the Settings link.
Open Validation Link
In the sidebar, click the Validate Links in Content button.
Start Link Validation
Click the Start Link Validation button.
If any links are found in the course, Canvas displays the name of the content item and the invalid link. To correct the error, click the name of the content item.
Please note: there is a possibility that you might get some false positives. From Canvas:
There are currently two cases in which a teacher may get a false positive result. Product is working to have both of these resolved soon.
If the link has a redirect.
If the link needs authentication that the canvas server does not posses (but the user does).
So you may find some "errors" on links that access information on the Portal or through the ezproxy and sites like that.