I have noticed that the way I use announcements in my online classes is very different from the way I use them in my traditional face-to-face classes. Unfortunately, Canvas does not really seem to be set up to make announcements easy to use for fully-online teachers. There are several things Instructure could do that would make announcements easier, and I have submitted a few feature ideas. They will be open for voting April 6 - July 6. I hope you will consider voting for some or all!
Thanks for your help!