I have Windows 10 installed in Boot Camp on my Mac running MacOS Sierra 10.12.5. I want to install Ubuntu on a disk partion .
Could I use Boot Runner to show all 3 volumes on startup and switch to each as i can with windows 10 and MacOS Sierra ?.
Definitely. If you can select it via the option key when starting up (or via the Startup Disk Prep pane), Boot Runner should be able to display and boot to it.
tim