We are trying to find a way to assign a letter grade to students' submission without giving them number grades. When we select the letter grade, the assignment still requires you to pick the total number of points and assigns a number based on the letter grade you pick. Will the students be able to see the number grades as well, or are the letter grades the only ones viewable to the students? Thanks!
Hi So Yeon Shin 
However, to answer your question, even with a letter grade students will, indeed, always be able to see the point equivalent in their view of Grades. This is shown here (see: How do I use grading schemes in a course? ) at the very last screen capture.
This is, indeed, a sore point with some fellow Canvas users. I would invite you check out the rather lively discussion here: Can't a letter grade just be a letter grade? and scroll down and check some of the other Feature Idea links that others have posted in that discussion.
Hope this helps at least clarify for you the way things are presently in Canvas.
Hello there, So Yeon Shin...
I wanted to check in with you because we have not heard back from you since you first posted this question on September 27th and then received some feedback from both Roxanne Conroy and Ken Black later that day. Have you had a chance to review the replies from Roxanne and Ken? Did either of their replies help to answer your question? Do you have any outstanding questions yet as it relates to your initial posting? If you feel that either Roxanne's or Ken's response has helped to answer your question, please go ahead and mark it as "Correct". However, if you are still looking for some help from members of the Canvas Community, please let us know by posting a message below so that we can continue to help you out. For now, I'm going to mark your question as "Assumed Answered", but this won't prevent you or others from posting additional comments or questions below which are related to this question. I hope that's alright with you. Looking forward to hearing back from you.
Hi there So Yeon Shin a belated
Welcome to the community!
I believe according to the What are grading schemes? guide, whatever you input will show as a letter grade to the student:
It will show how much they got out of whatever your point system indicates, as well as provide the letter grade. Here are some examples from my sandbox after testing