Canvas: How to Link to an Individual Discussion Post
In a Canvas discussion, use the search box at the top of the discussion to perform a search for a name or keyword in the individual post
The posts that appear in the search results will each have a "View in Discussion" link at the bottom which includes a permalink to that particular post.
Right-click or control+click that link to see a pop-up menu
Select "Copy Link Location" from that pop-up menu (wording may vary depending on which web browser you're using), which will copy the post's URL to your computer's clipboard