@NickChevalierUT
Can you share more details about what you are trying to accomplish? It would be useful to know more about why you are looking for an alternative and why submitting and assessing directly in Canvas hasn't worked.
If you have the resources and technical expertise, it should be possible to set-up an automated process to detect submissions in a specific course and retrieve the files. The List Assignment Submissions endpoint is what you would need to get the submissions for a specific assignment in a specific course. You would then need code to download the linked files and a process to upload them to the other service you want to use.
Alternatively, you could also just wait for all student submissions to be turned in or wait until after the due date and download all student submissions in a zip folder. How do I download all student submissions for an assignment?