At the Canvas administrator level, under their "Settings" menu >> "Settings" tab, there is a check-box option for "Disable uploads to Canvas Media from the enhanced rich content editor". I am not sure if this is exactly what you would be looking for, but you might want to have a conversation with your school's Canvas administrator about this. Keep in mind that turning this option on would not only affect your course, but it would affect all other instructors who teach courses in your Canvas environment...and some of those instructors might wonder what happened to that option in the RCE. Here is the admin Guide for your reference: