I found the Movie Studio help useful in understanding how to work with 3D media; you should look it over.
The key point is to ensure that the project properties have the Stereoscopic 3D mode set to one of the choices other than "Off". Once this is done, 3D media can be automatically recognized as it is added to the project. If it is not automatically recognized, the properties for the media can be revised to tell the software what type of 3D media it is.
I do use Movie Studio 13 suite but it only recognises AVCHD, 960x1080/60i.
MP4(MVC) file,1920x1080/60i Full HDx2ch, is not recognised as 3D dispite turning stereoscopic 3D mode on and trying all the choices but it does not turn 3D on just mono. Max Pow
I have not worked with MVC contained in MP4, only with the dual stream MTS files created by the Sony TD10; and with individual left/right still-image sequences. You many need to convert the MP4 media to another format to be able to import it into Movie Studio.
Not (convert) but remux with something like (tsMuxeR).
*.m2ts; *.mts; *.mp4 etc. are containers. We might hate it but we forced to crutch edit/output file to make it readable by Movie Studio and for suitable output.
Cheers, A87