UI_Popup

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class UI_Popup : UI_Base
{
    public virtual void init()
    {
        Managers.UI.SetCanvas(gameObject, true);
    }

    public virtual void ClosePopupUI()
    {
        Managers.UI.ClosePopupUI(this);
    }
}

UI_Scene

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class UI_Scene : UI_Base
{
    public virtual void init()
    {
        Managers.UI.SetCanvas(gameObject, false);
    }
}

UI_Manager

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class UIManager
{
    int _order = 10;

    Stack<UI_Popup> _popupStack = new Stack<UI_Popup>();
    UI_Scene _sceneUI = null;

    public GameObject Root
    {
        get
        {
            GameObject root = GameObject.Find("@UI_Root");
            if (root == null)
                root = new GameObject { name = "@UI_Root" };
            return root;
        }
    }
    public void SetCanvas(GameObject go, bool sort = true)
    {
        Canvas canvas = Util.GetOrAddComponent<Canvas>(go);
        canvas.renderMode = RenderMode.ScreenSpaceOverlay;
        canvas.overrideSorting = true;

        if (sort)
        {
            canvas.sortingOrder = _order;
            _order++;
        }
        else
        {
            canvas.sortingOrder = 0;
        }
    }

    public T ShowSceneUI<T>(string name = null) where T : UI_Scene
    {
        if (string.IsNullOrEmpty(name))
            name = typeof(T).Name;

        GameObject go = Managers.Resource.Instantiate($"UI/Scene/{name}");

        T SceneUI = Util.GetOrAddComponent<T>(go);
        _sceneUI = SceneUI;

        go.transform.SetParent(Root.transform);

        return SceneUI;
    }

    public T ShowPopupUI<T> (string name = null) where T : UI_Popup
    {
        if (string.IsNullOrEmpty (name))
            name = typeof (T).Name;

        GameObject go = Managers.Resource.Instantiate($"UI/Popup/{name}");

        T popup = Util.GetOrAddComponent<T>(go);
        _popupStack.Push(popup);

        go.transform.SetParent(Root.transform);

        return popup;
    }

    public void ClosePopupUI(UI_Popup popup)
    {
        if(_popupStack.Count == 0)
            return;

        if (_popupStack.Peek() != popup)
        {
            Debug.Log("Close Popup Failed");
            return;
        }

        ClosePopupUI();
    }

    public void ClosePopupUI()
    {
        if (_popupStack.Count == 0)
            return;

        UI_Popup popup = _popupStack.Pop();
        Managers.Resource.Destroy(popup.gameObject);
        popup = null;

        _order--;
    }

    public void CloseAllPopupUI()
    {
        while (_popupStack.Count > 0)
            ClosePopupUI();
    }
}

스택을 이용해 팝업 UI를 관리한다. 씬 UI같은 경우에는 스택이 필요가 없으므로 스택을 사용하지 않는다.

또한 객체들을 씬 내에서 정리하기 위해 Root라는 프로퍼티를 사용해 게임이 실행될 때 씬 내에서 Root 객체 내에 저장되게 하였다.