WPF only supports bounding box intersection methods between Rect3D objects, i.e. solid rectangles. ModelVisual3D objects are generally used to render Model3D objects, which present a Bounds property. You can use this to check for intersection:
ModelVisual3D modelVisual = new ModelVisual3D();
// set your modelVisual
Model3D geomModel = (Model3D)modelVisual.Content;
Rect3D bb = geomModel.Bounds;
Rect3D rect = new Rect3D();
// set your rect
bool isIntersecting = rect.IntersectsWith(bb);
If you need finer collision detection, you better use some more sofisticated tools, for instance BulletSharp, the C# wrapper of Bullet Physics. Have a look at this previous post.