Unity - Move Canvas as a 3D GameObject

I have a script with which i can move (on 2 axis) any 3D objects, the script i'm using is this (for mouse and touchscreen)

 using UnityEngine;
 public class DragInput : MonoBehaviour {
 
   
 
     GameObject gObj = null;
     Plane objPlane;
     Vector3 mO;
     Camera cam;
 
     void Awake() {
         cam = GameObject.FindGameObjectWithTag("MyCamera").GetComponent<Camera>();
     }
     Ray GenerateMouseRay()
     {
         Vector3 mousePosFar = new Vector3(Input.mousePosition.x,Input.mousePosition.y,cam.farClipPlane);
         Vector3 mousePosNear = new Vector3(Input.mousePosition.x,Input.mousePosition.y,cam.nearClipPlane);
         Vector3 mousePosF = cam.ScreenToWorldPoint(mousePosFar);
         Vector3 mousePosN = cam.ScreenToWorldPoint(mousePosNear);
 
         Ray mr = new Ray(mousePosN, mousePosF-mousePosN);
         return mr;
     }
 
     // Update is called once per frame
     void Update () 
     {
         if(Input.GetMouseButtonDown(0))
         {
             Ray mouseRay = GenerateMouseRay();
             RaycastHit hit;
 
             if (Physics.Raycast(mouseRay.origin, mouseRay.direction, out hit))
             {
                 gObj = hit.transform.gameObject;
                 objPlane = new Plane(cam.transform.forward*-1, gObj.transform.position);
 
                 //calc mouse offset
                 Ray mRay = cam.ScreenPointToRay(Input.mousePosition);
                 float rayDistance;
                 objPlane.Raycast(mRay, out rayDistance);
                 mO = gObj.transform.position - mRay.GetPoint(rayDistance);
             }
         }
         else if(Input.GetMouseButton(0) && gObj)
         {
             Ray mRay = cam.ScreenPointToRay(Input.mousePosition);
             float rayDistance;
             if (objPlane.Raycast(mRay, out rayDistance))
                 gObj.transform.position = mRay.GetPoint(rayDistance) + mO;
         }
         else if (Input.GetMouseButtonUp(0) && gObj)
         {
             gObj = null;
         }
     }
  }

If i click on any object i have created (with a box collider) i can freely move this object over the screen. Unfortunately this will not happen if the object is a World Space UI(canvas). Anyone can gime me some hint and tell me why i'm not able to move the space UI?