CODE EXAMPLE FOR CSHARP

mouse position to canvas transform

Vector3 GetMousePosition() {
        Vector2 movePos;
        RectTransformUtility.ScreenPointToLocalPointInRectangle(
            parentCanvas.transform as RectTransform,
            Input.mousePosition, parentCanvas.worldCamera,
            out movePos);
        Vector3 positionToReturn = parentCanvas.transform.TransformPoint(movePos);
        positionToReturn.z = parentCanvas.transform.position.z - 0.01f;
        return positionToReturn;
    }