I noticed this topic is somewhat dated, but just in case anyone is still looking for an answer on the Eagle PCB render, here is my experience with this topic;
At first it seems quite straight forward, design the PCB in Eagle, click on Export to Fusion360 and that seems to do the trick. The catch is that if you used components from libraries you imported, the quality of the render depends fully on whether or not your component libraries include 3D models.
If not, Fusion360 will simply render a “flat box shape” the size and shape of the footprint. I usually render the PCB only (with signals) in Fusion and then revert back to sites like Grabcad for properly rendered components. I have attached two examples, a straight forward Eagle to Fusion render and then one I did including renders sourced from Grabcad and ‘assembled’ in Rhino.
Directly exported form Eagle to Fusion360 (no further rendering applied)
PCB rendered to Fusion360 then imported all components individually from Grabcad and assembled in Rhino.
This is by no means law, simply my experience with this topic. Best of luck !