Every semester dozens and dozens of students who do not turn in assignments send me frantic and often angry emails explaining that they did submit on time or the internet was acting funny or some other excuse (the digital equivalent of my cat ate the homework). I have a firm policy of not accepting late assignments regardless of the reason, but the students often leave their interaction with me frustrated and angry at me for their mistake. If Canvas autogenerated a receipt to the student's email account that their assignment was submitted, then the students could forward me their receipt to clear up any issues. However, I believe that the students are responsible for their issues about 99.9% of the time and that they would not have a receipt for a non-submitted assignment, but the act of them looking through their records and seeing no receipt of submission would go along way toward proving that the mistake was on their end and the late assignment was totally preventable. At the end of the day, I am eager to provide my students with more avenues for accountability rather than them blaming my course policies, which this email receipt would provide.
I know that the students receive a message on their canvas page that says their assignment was submitted, but short of requiring students to take a screen capture image of that as insurance, my students have no recourse.
There is a feature idea open for voting that is asking for just that! You can check it out at https://community.canvaslms.com/ideas/3455-e-mail-confirmation-upon-assignment-submission
If this is what you are looking for, please join the discussion and support by voting.
I should also add that the existing submission receipt is available to students forever, and so they could simply go back to the specific assignment and do a simple screen-shot that they could then submit to you as proof.