Example of a game with 3 canvas layers.

layers.html

<div id="stage">
    <canvas id="ui-layer" width="480" height="320"></canvas>
    <canvas id="game-layer" width="480" height="320"></canvas>
    <canvas id="background-layer" width="480" height="320"></canvas>
</div>

<style>
#stage { 
    width: 480px; 
    height: 320px; 
    position: relative; 
    border: 2px solid black 
}

canvas { position: absolute; }
#ui-layer { z-index: 3 }
#game-layer { z-index: 2 }
#background-layer { z-index: 1 }
</style>