It is now possible to exclude a Canvas graded assignment from the final grade.
Note: this is possible for assignments, but not for discussions or quizzes.
The setting is found in any assignment Edit view under the Settings tab.
Tip: this would be a good feature to use when you want students to be able to test a paper in Turnitin before submitting the final paper to you.
To make this work, under the assignment’s Turnitin optional settings, set the Allow students to view Originality Reports? to yes and scroll down and click Submit.