Hi, @laura2 , given the specialized subject matter of your question, we've moved it to the Instructional Designers group. If you're not yet a member of that group, you can easily join by clicking on the link to the group and selecting Join Group from the Actions dropdown you'll see at the upper right of the group home page.
And thanks, @bneporadny , for finding and responding to this question; if you're not yet a member of Instructional Designers, please join! 
Thanks all. Laura Gibbs, can you give me an example of a publicly-available site that does allow iframe embedding, so I can test it to make sure it's not a problem on my end? I was only using the Khan Academy site as an example, but maybe blocking iframe display is so common that every dummy site I've tried it with has the same issue.
I do not, at this time, wish to embed my own content (for example, from another blog or site that I write/control). Most of the tutorials I've seen on iframe embedding use self-created, off-Canvas content in their examples, but say it will work the same way "for any web page." That hasn't been my experience.
As to why I want to do it this way, there are usually three reasons:
- Continuity. My students do all the homework and reading at home (flipped classroom for homeschoolers who only meet once a week for one hour per class). They usually have 3-5 main readings or video assignments, which I include as links from a single content page. This comes after 2 or 3 content pages with shorter/easier introductory material. Keeping all of the introductory material inside Canvas is one way I distinguish between the types of reading they need to do, and with it the types of reading strategies they need to employ. I've noticed that class preparation and participation has gone up when the homework is set up in this very methodical way: they go through the modules 1, 2, 3, 4, etc. until they get to the last page which has the "real" assignment with all the external links.
- Control. I would love to be able to add text above or below embedded content. If I can't do that, I'll link from a content page and include my own commentary -- either something as simple as "read this article from The New York Times: [link]" or a paragraph or so explaining what I'm linking to, why, and which parts they should pay attention to. I'm willing to keep doing that until the end of my days, but it'd be cool if I could make the modules snazzier by putting the content itself right inside the page. (This is why I don't use the external link tool at all; it's the worst of both worlds. Off-Canvas linking, AND no way to contextualize it.)
- Pre-empting student laziness. I have a few students who just don't click on links! It's hard enough to get them to log into Canvas every week; asking them to press all these extra buttons sends them into despair, apparently.
I can't even say I'm that different. I don't click on everything I see while scrolling through social media; I need to believe it's going to be worth my time. Putting the content right there in front of them raises the odds that they'll at least skim it.
I don't teach in a graded environment, so I don't have any sticks to get my students to do the work. Only carrots. Embedding content would make the modules more visually interesting without becoming more confusing in the process.
