You can create an event listener for the select event and use the row and column data returned from the event to get the URL information from your DataTable object. You can then set window.location to the URL and it will be as if the user clicked a link. As an example:
/* assumes:
* data is the DataTable object
* chart is the chart object
* URL's are stored as a property, named "URL", of the cells
*/
new google.visualization.events.addListener(chart, 'select', function() {
var selection = chart.getSelection()[0];
window.location = data.getProperty(selection.row, selection.column, "URL");
});