create 360 from 2d video adding background

I have a 2D video and I would like to move it into 360. I'm aware of the differences and so on and so forth but, I would like to have a 360 video with something like a cinema room and, in the main screen, that 2D video would be displayed.

Is there any suggestion, automatic tool for that, or anything that could be useful? I'm open to use Unity3D, blender or any software related to video editing.

The usual approach is to use a computer generated world or a 360 image for the cinema room rather than a 360 video, and display your 'flat' 2D video on a 'screen' or wall in that generated room.

You basically render the video onto a texture that you have set up in Unity. This is supported as standard by Google VR for unity(https://developers.google.com/vr/develop/unity/video-overview):

Streaming Video Support

The GVR SDK for Unity includes an additional GVR video plugin that supports streaming flat and 360° videos in both mono and stereo formats by using the ExoPlayer library to handle decoding and rendering of video, audio, and related streams. ExoPlayer provides all the standard playback framework for both videos embedded in your application and streaming videos, including adaptive streaming support, such as DASH and HLS.

For example the Netflix version, VR Theatre, looks like this - the video plays on the 'screen' in front of the viewer:

If you look on the unity asset store you can find complete home or cinema 360 'images' that you can use in Unity also - for example (at the time of writing): https://assetstore.unity.com/packages/templates/vr-home-cinema-66863