Maybe I am wrong here as I do have a Roku as well…
I allow Alexa direct control of one of my Fire TVs so I could say turn up/down the volume and a couple of other commands. For this Fire TV, I did not select the Harmony Activities to be discovered by Alexa via ST. I could have sworn that the extra channels then appeared in the Alexa App such as HBO Now, Hulu and blah blah blah.
This couldn’t have come from the Roku because there is not direct connection from Roku to Alexa…
Amazon updated the Alexa/fire TV integration a few months ago and you can now launch individual apps and channels on fire TV without needing to have a Harmony involved. It works very well from a voice command.
So you can now say “Alexa, watch Mr. Robot on PlayStation Vue” where PlayStation vue is an app on your fire TV. Or “Alexa, watch Stranger Things on Netflix”
However, as others have mentioned, you cannot include these actions in an Alexa routine yet. I’m sure that will come eventually because everybody wants to see it, but as of now, there are only a few things you can put into an Alexa routine and fire TV actions are not one of those.
Workaround 1: Use Alexa to run a Harmony “scene” that runs Netflix on Roku
There are two workarounds. The first does require a Logitech Harmony and the Roku, which is good if you already have those, but if you don’t I don’t think they’re worth buying at this point as I do expect Amazon to add more functionality to the fire TV in this regard.
Workaround 2: Use Alexa to flip a virtual switch in SmartThings which triggers a different speaker device to say a specific phrase that Alexa will hear
The second is kludgy, but works. You can set up a second device which does allow you to automate what it says, and then have IT speak back to the echo to trigger your next commands. So that when the human says “movie night“ Alexa flips a switch which triggers a different device to then say “Alexa, watch Netflix”
My personal advice would be just to wait a few months, it’s very likely that Amazon will add this capability to the base fire TV/Alexa integration. But if you really need it in an Alexa routine right now, the Harmony/Roku option will work the most smoothly and feel the most natural.