HideShowCanvas.cs

using UnityEngine;
using UnityEditor;
using UnityEngine.UI;
using System.Collections;
using System.Linq;

[InitializeOnLoad]
public class HideShowCanvas : Editor
{
	static HideShowCanvas()
	{
		EditorApplication.playmodeStateChanged += PlaymodeStateChanged;
	}

	static void PlaymodeStateChanged()
	{
		Canvas canvas = (Canvas) Resources.FindObjectsOfTypeAll(typeof(Canvas)).FirstOrDefault();
		
		if(canvas == null)
			return;

		if(EditorApplication.isPlayingOrWillChangePlaymode)
		{
			canvas.gameObject.SetActive(true);
		}
		else
		{
			if( EditorPrefs.GetBool("DO_HIDE_CANVAS") )
				canvas.gameObject.SetActive(false);
		}
	}

	[MenuItem("Edit/Toggle Canvas &c")]
	static void Toggle()
	{
		Canvas canvas = (Canvas) Resources.FindObjectsOfTypeAll(typeof(Canvas)).FirstOrDefault();
		canvas.gameObject.SetActive(!canvas.gameObject.activeSelf);
		EditorPrefs.SetBool("DO_HIDE_CANVAS", !canvas.gameObject.activeSelf);
	}
}