Edit in JSFiddle

function go() {
    map = L.map("map").setView([48.845, 2.424], 5);
    var lyrOSM= L.tileLayer('http://{s}.tile.osm.org/{z}/{x}/{y}.png?') ;
    var lyrOrtho = L.geoportalLayer.WMTS({
        layer: "ORTHOIMAGERY.ORTHOPHOTOS",
    });
    var lyrMaps = L.geoportalLayer.WMTS({
        layer: "GEOGRAPHICALGRIDSYSTEMS.MAPS",
    }, { // leafletParams
        opacity: 0.7
    });

    map.addLayer(lyrOrtho);
    map.addLayer(lyrOSM) ;
    map.addLayer(lyrMaps) ;
    var layerSwitcher = L.geoportalControl.LayerSwitcher({
    	layers : [{
        	layer : lyrOSM,
            config : {
            	title : "OSM",
                description : "Couche Open Street Maps"
            }
        }]
    });
	map.addControl(layerSwitcher);

}

Gp.Services.getConfig({
    apiKey : "jhyvi0fgmnuxvfv0zjzorvdn",
    onSuccess : go
}) ;

var infoDiv= document.getElementById("info") ;
infoDiv.innerHTML= "<p> Extension Leaflet version "+Gp.leafletExtVersion+" ("+Gp.leafletExtDate+")</p>" ;
<div id="map"></div>
<div id="info"></div>
#map {
    padding: 5px;
    width: 100%;
    height: 300px;
    box-shadow: 0 0 10px #999;
}

#info {
    padding: 5px;
    width: 100%;
    height: 20px;
    font-family: monospace;
}