Canvas allows students to submit as many times as they like before the deadline, whereas our regulations only allow the final version to be submitted.
If you are allowing students to submit drafts, if they don't upload a modified version before the deadline, the last draft becomes the on-time submission.
If a teacher marks an earlier submission the draft and feedback remain accessible (teachers see these in a drop down box) - what the student sees is dependant on whether grades have been posted.
Not sure how this translates into peer review. The line of least resistance could be to set up a draft assignment for peer review with an earlier deadline, then a final submission point for teacher grading ??