That's super intrusive. I'm guessing that your school board is full of zealous right-wingers who want to make sure that teachers aren't teaching anything "objectionable." I would not want to facilitate this.
If the school board just wants to see what Canvas is like, make a PowerPoint presentation about the features of the LMS. Alternatively, you can create a mock course for them to look at.
However, if you are going to give them direct access into an individual teacher's course content, then you really need to long and hard about this. It is an unreasonable request. As a teacher, I would feel very uncomfortable with this.
This is not a question of how to grant this access, but rather whether to grant this access. There are philosophical questions to address beyond the technical ones.