I have tried this for one record i am getting all sucessfully,Just pass the selected record id from listviewbutton javascript code in querystring parameters.

   apex/googlepage?id='Selected ID';

Then there get the id into controller using apexpagereference class.

like apex.

       :ApexPages.currentPage().getParameters().get('id')

And Declare a property in java script of the googlemappage

         like  var Addr={!address};

Query the address from selected object and assign address to addr property in controller.

then you will get .

i am giving code samples use them.

for marker

marker.openInfoWindowHtml("<div style=\"float:left;\"><div style=\"font-family: arial, san-serif; padding-left:30px;\"><span style=\"font-weight:bold;\">{!Contact.Name}</span><br/>{!Contact.MailingStreet}<br/>{!Contact.MailingCity}, {!Contact.MailingState} {!Contact.MailingPostalCode}<br/><br/></div></div>");

Use this sample.

  

<apex:page showHeader="false" sidebar="false" standardController="Contact" extensions="contactMap">
    <script type="text/javascript" src="http://www.google.com/jsapi?key=ABQIAAAAJeLmMRtO1d8ECMSZkNslVBQ1QIMfevrNmxgjfvD_9mfSx071yRTVaO0JM4GCg9irT4OmXn0jUgI6gQ"></script>
    <script type="text/javascript">
        google.load("maps", "2.x");
        
        var addressPoint;
        
        // Call this function when the page has been loaded
        function initialize() {
            if (GBrowserIsCompatible()) {
                var map = new google.maps.Map2(document.getElementById("map"));
                map.addControl(new GSmallMapControl()); 
                
                var address ="{!Address}";

                var geocoder = new GClientGeocoder();
                geocoder.getLatLng(address, function(newPoint) {
                    if (!newPoint) {
                        $('#textAddress').html('Bummer! We couldn\'t find the location you have in the Mailing Address field. Try entering a new address and reloading the page...');
                    } else {
                        map.setCenter(newPoint, 14);
                        map.addOverlay(new GMarker(newPoint)); 
                        var marker = new GMarker(newPoint); 
                        map.addOverlay(marker); 
                        marker.openInfoWindowHtml("<div style=\"float:left;\"><div style=\"font-family: arial, san-serif; padding-left:30px;\"><span style=\"font-weight:bold;\">{!Contact.Name}</span><br/>{!Contact.MailingStreet}<br/>{!Contact.MailingCity}, {!Contact.MailingState} {!Contact.MailingPostalCode}<br/><br/></div></div>");
                    }
                });
            }
        }
                
        google.setOnLoadCallback(initialize);
    </script> 
     <style>
        .locationGoogleMap {
            color:#4A4A56;
            font-family:arial,helvetica,sans-serif;
            font-size:12px;
            font-weight:bold;
            left:24.3%;
            position:relative;
        }
        
        #textAddress {
            color:#000000;
            font-family:arial,helvetica,sans-serif;
            font-size:18px;
            height:20px;
            left:40%;
            position:relative;
        }       
    </style>
    
    <apex:outputpanel id="googleMap" layout="none">
        <span id="textAddress"></span>
            <div id="contentMap" style="width: 100%; position:relative; margin-top:10px;"> 
                <div id="map" style="height: 300px;"></div>
            </div>
    </apex:outputpanel>
</apex:page> 



Controller