Any time you change the teacher associated to the course in PowerSchool, it is going to create a new course in Canvas and move the section and it's enrollments to that new course. At that point, you can cross-list the section back into its old course and all of the grades and submissions will return and no future changes to the teacher will move the section because cross-listing makes the section association sticky. 

In Canvas, go to Settings --> Sections of the new course. On the right, there is a button that says "Cross List this Section". Click that and type in the course ID number of the original course you want to place the data. This will restore the first course to its original state.