Hello All. Some thoughts to share here. All of this is possible, but remember (I learned this the hard way) that iframes don't ever allow any cross-domain data sharing. Meaning that your procotoring iframe can absolutely exist on it's own, but will not get live data such as mouse movements, scroll etc, from the main canvas page--unless you create a separate script and embed in the Canvas template specifically to connect the two.
Otherwise you will essentially need to enable content-item delivery (LTI 1.1) or deep linking (LTI 1.3), and enable the app to show up in the rich text editor so that you can select a specific link and return it using the content-item delivery spec. Honestly I am stuck on this a bit myself, so if anyone can offer guidance around a comprehensible interpretation of content-item delivery where the user selects from a series of links in the RCE modal and the item is delivered back to the RCE in an iframe that would be excellent.