first Thank you for the help,
just so you can see what I'm trying to do I've posted this image and from what I understand from your answer is I add the high using surface selection and paint and bake Note high poly is 2.5 million polys so that should be fine for the detail painting then bake it out. then do the same for the low poly retopo mesh add new seam unwrap and that's it. I guess my confusion in this is that in blender you place the Hi Over the Unwrapped Low and bake to that specific map. I'm trying to understand how the hi poly map will be same layout as the low once its unwrapped in 3d coat ?