CameraFinder.cs

using UnityEngine;

namespace App
{
    public class CameraFinder : MonoBehaviour
    {
        public Camera DisposeCamera;
        private Canvas _canvas;

        // Use this for initialization
        void Start()
        {
            this._canvas = this.GetComponent<Canvas>();

            if (Camera.main != null
                && this.DisposeCamera != null
                && !System.Object.ReferenceEquals(this.DisposeCamera, Camera.main))
            {
                this._canvas.worldCamera = Camera.main;
                Destroy(this.DisposeCamera.gameObject);
            }
        }
    }
}

SceneManager.cs

using UnityEngine.SceneManagement;

namespace App
{
    public class SceneManager : SingletonMonoBehaviour<SceneManager>
    {
        public void Replace(string name)
        {
            UnityEngine.SceneManagement.SceneManager.LoadScene(name, LoadSceneMode.Single);
        }

        public void Hover(string name)
        {
            if (!UnityEngine.SceneManagement.SceneManager.GetSceneByName(name).isLoaded)
            {
                UnityEngine.SceneManagement.SceneManager.LoadScene(name, LoadSceneMode.Additive);
            }
        }

        public void Dispose(string name)
        {
            if (UnityEngine.SceneManagement.SceneManager.GetSceneByName(name).isLoaded)
            {
                UnityEngine.SceneManagement.SceneManager.UnloadScene(name);
            }
        }
    }
}

SingletonMonoBehaviour.cs

using UnityEngine;

namespace App
{
    public class SingletonMonoBehaviour<T> : MonoBehaviour where T : SingletonMonoBehaviour<T>
    {
        protected static T instance;

        public static T Instance
        {
            get
            {
                if (instance == null)
                {
                    instance = (T) FindObjectOfType(typeof(T));

                    if (instance == null)
                    {
                        Debug.LogWarning(typeof(T) + "is nothing");
                    }
                }

                return instance;
            }
        }

        protected void Awake()
        {
            CheckInstance();
        }

        protected bool CheckInstance()
        {
            if (instance == null)
            {
                instance = (T) this;
                return true;
            }
            else if (Instance == this)
            {
                return true;
            }

            Destroy(this);
            return false;
        }
    }
}