This article lists recommended practices for extra credit in Canvas.
Create a new assignment with zero points possible  and select any submission type . Assignments set to the No Submission type work well for classroom activities, such as in-class discussions or presentations.
After students complete an online submission or complete and submit work offline, you can add and adjust points in the Gradebook.
Note: For a zero point assignment to factor into a student's grade, you must add at least one additional graded assignment with a positive point value. This additional assignment can be in any assignment group.
Add extra points to an Assignment you've already created. Manually enter the extra points in the Gradebook.
For example, this assignment is worth 30 points. Adding 5 extra points will bring the assignment total for this student to 35 points. The added points will increase total points calculated in the Gradebook's final grade.
Add an additional Criterion to a Rubric for extra credit. Make sure you make the rubric worth more than the assignment and you can give students extra points or not without affecting the actual assignment points.
When assignment groups are weighted, Canvas will not calculate grades for an entire group that has no points possible. Therefore, for extra credit assignments to calculate correctly in weighted groups, they must be housed within an existing assignment group that has at least one assignment worth more than zero points.
In this example, the extra credit assignment is housed within the Extra Credit assignment group with multiple assignments worth more than zero points . Notice that the assignment groups weights total 110% . Any assignment placed within the Extra Credit assignment group will have either a positive or neutral effect on your students' overall grade. Additionally, if a student does not submit the extra credit assignment, their grade will not be negatively impacted.
When the student completes the work required for the extra credit assignments, you can manually add points to the Gradebook.
For more information on extra credit options in Canvas, see: Canvas - How do I give extra credit in a course?