The discussion boards in Canvas can be used for several reasons:

Allows every person in the course to contribute to the discussion – even students who are less likely to speak out in class
Students have more time to reflect on their responses
Allows you to ask a question that was sparked by an in-class discussion
Allows you to assign small groups to work on answers to complex questions and then post their answers
Can be used for students to ask open-ended questions about the course's concepts
Like any good question, discussion board questions can ask students to apply or explain concepts that they are learning in the course
Ask students to email questions for the board and select a few for a deeper level of student engagement.