The short answer is that you, as a student, cannot change the Course End Date or the due dates of Assignments. 

The Course End Date will most likely be set by your school. The Assignment due dates will be set by your professor.  Taking a course on Canvas has the same basic parameters as taking a face-to-face class.

It's really great that you are thinking ahead about your course workload. Your responsibility as a student is to figure out how you can meet the course requirements set by your instructor and your school.

Good luck!