Something strange happens when web links migrate from Blackboard to Canvas, they become unavailable (unpublished) to students in Canvas despite the availability settings you had set in Blackboard.
To fix this and allow your students to view the link you will need to publish any web links you have in your course.
1. Navigate to the link location
2. If you do see a green check mark on the right hand side it is not published. Click the grey circle with a line through it to publish.