Hi, from what I understand, the difference you are seeing between the two applications is caused by the Render settings, not the Camera itslef. Basically, Render settings are not transfered through the FBX format. This means that you must make sure you are using the same render settings (resolution, etc.) in both apps.
Here is an example of what I mean:
In Maya, look at the resolution you are using in your Render settings. Let’s say it’s set to 640x480. Export this to FBX. In Motionbuilder, load the file. By default, MB sets the “Picture Format” in your Render Settings to “From Camera”. By default, MB sets your viewport “Resolution” to “Window Size”. This means that you are rendering the viewport resolution, which is much wider (fisheye) then the resolution previously used in Maya.
To correct this, simply change your Render Settings for the “Picture Format” in MotionBuilder to match the resolution set in Maya, in this example, 640x480.
You could also change the Camera Settings for the “Picture Format” to this resolution to view the correct resolution directly in the viewport as well.
Hope this helps!