With Sketchfab, you can add a model embed to your assets in the Unity3D marketplace.
Not only do we support direct export of assets from Unity with our Unity to Sketchfab Exporter, we also support direct file export from the most popular modeling tools in the industry.
Once you've uploaded your 3D model to Skecthfab, you can head to the Insert Audio/Video dialog in Unity3D marketplace and choose Sketchfab from the Service drop-down. Once there, enter your model URL in the URL field.
See also Unity Connect.