@LisaCoyne ...
One way you could possibly do this is by making a "master" course via Canvas Blueprint courses. Then, you could sync this "master" course to your "child courses"...which then copies all the course content out to each course. You might want to talk with your school's Canvas administrator about the use of Blueprint courses to see if this might be an option.
Another option might be to use Canvas Commons. You could share your assignment out to Canvas Commons. Then, as long as you are enrolled in the other courses, you could import that assignment into all the other courses at one time directly from Commons. One of the nice things about this is that if you needed to make a change to any part of that assignment, you would make the change to the original course, re-share it to Commons, and then Commons would ask you if you want to update the other courses for you. It's kind of an "update once, distribute to many" idea.
Do you think either of these options might work for your needs? Keep Community members posted...thanks!