Best answer by melvimbe
The below link is the list of Alexa commands you can use with Sonos related to music and TV functions.
I could have sworn that you can give a command like 'Alexa, switch to HDMI 3' was possible, but I don't see it listed here. I recalling trying it myself when I originally got a Beam, but it did not work because my Samsung TV did not support the command. CEC commands are a little hit and miss because your TV and connected devices (Beam) are not required to support specific commands, or support them in every condition.
I can't say whether Vizio TVs support HDMI switching via CEC commands, but I would not be too surprised if they didn't. It doesn't seem to be a popular command to support. However, devices that use IR commands (like a TV remote) to switch HDMI will work quite well in almost situations. Logitech Harmony and Amazon's FireTV cube are good examples of this.