@AUBREYROBERTSON ...
Unfortunately, there's nothing that I'm aware of within the Canvas UI (User Interface) that would allow you to upload rubric scores/comments used as student feedback via an Excel spreadsheet. Interesting idea, though. You could certainly submit this as an Idea to see what kind of feedback you'd receive.
Canvas Ideas and Themes - Instructure Community (canvaslms.com)
Click on the blue "View and Submit Ideas" button, and then click on the blue "Submit an Idea" button. Or, just go here:
Canvas Ideas - Instructure Community (canvaslms.com)
Also, please review the Guides under the heading "Ideas and Themes" to see how the idea process works and how to submit an idea:
Instructure Community Guide - Instructure Community (canvaslms.com)
Hope this helps in some way.