In Canvas you will need to weight grades according to "assignment groups" (eg., "Discussions" is an assignment group). You cannot weight the specific assignment itself, but rather the category or assignment group that it belongs to. You can create new assignment groups as needed. If you want to weight an individual assignment, such as a midterm paper, you will need to give it its own assignment group.

Further resources:

• How do I create Assignment Weights?
• How do I weight the final course grade based on assignment groups?
• How do I add an assignment group in a course?
• How do I change assignment group weights in the Gradebook?