I am not aware of an automatic grader. I'm not sure I would trust something automatic to confirm that an essay contain an accurate response. Grammar and plagiarism on the other hand might be possible.
If you use turnitin for plagiarism you might like to comment in: https://community.canvaslms.com/t5/Idea-Conversations/New-Quizzes-Allow-use-of-turnitin/idi-p/331350
Otherwise you might like to comment on: https://community.canvaslms.com/t5/Idea-Conversations/Download-essay-questions/idi-p/319728 which would allow instructors to quickly download all essay responses for submission to whichever plagiarism checker the school subscribes to.
Our school uses grammarly.edu (the .edu is important to differentiate from normal grammarly) for plagiarism, because it also provides some automatic grammar feedback to students. It is good at spotting sentences that need work, but not always correct about the best way to fix the sentence. I suggested an idea for integrating that with canvas, but in this new community it seems to have landed in something called "colder storage" that I do not have access to. I guess canvas does not want to integrate with grammarly. That's too bad, but we can still download student submissions from canvas and upload them into grammarly.edu, check for grammar and plagiarism both in that program, save a report and attach that report to comments in canvas.