It should be possible (and is in other systems, and was with a Canvas work-around that was mysteriously removed some months back) to sort posts within a discussion in such a way as to have a desired instructor authored post remain at the top of the discussion so every student would see it first when going to that discussion. This functionality in invaluable: this allows the instructor to write a summary post at the end of a discussion period and then have that post remain at the top of the discussion, so though written last would be seen first and clearly, not buried at the bottom of the discussion threads.
There was a Canvas work-around that allowed for this functionality that was taken away. It was possible when editing a discussion to click on "allow liking", then "only graders can like" and then "sort by likes." This allowed the instructor to author a post, "like" it, then click sort by likes and that instructor authored post would go to the top, since only the grader could "like" a post. For some mysterious reason, Canvas eliminated the "sort by likes" option, and so this functionality is no longer in Canvas (and other systems had easier ways to do this without such a work-around). The sort by likes option below the "allow liking" should be restored (again it is a mystery as to why it was removed) or some other means of sorting posts that would allow an instructor to put a specific post permanently at the top of a discussion should be available.
Added to Theme
Improve the user experience with discussions to provide for more meaningful discourse among course participants Theme Status: In Development