The Canon driver can detect and control more than one camera, but the Ekos configuration seems to only let me choose one to work work. I realize that multiple cameras is not a "normal" thing for most people, but when using cameras and lenses it's very convenience. I've traditionally just used an intervalometer and captured to the SD cards, but last year switched to Backyard EOS which can handle multiple cameras, either independently or synchronized.

So, I was excited when I saw that INDI/Ekos could handle multiple cameras. But so far, I don't see how to set up to actually control multiple cameras when it comes to running an exposure plan. I've only played with this indoors at this point, so maybe it's just a learning curve, but the page on DSLRs (www.indilib.org/devices/cameras/gphoto.html) that I found doesn't talk about this. And the fact that I effectively have a primary/secondary scope (plus a guider) means most of the setup isn't quite appropriate for this configuration.

Is it possible to run with dual "primary" cameras?

There has been some discussion on strategies for controlling multiple cameras but it will require a great deal of work to implement. So as of now, synchronized imaging is not supported at this time.

Adding to that: Ekos only allows for one primary camera. If you want to use more than one camera at a time, you will need to use multiple instances of Ekos which require multiple instances of INDI server. I am not sure if that can be run on a single computer.