fontFamily: String

Sets the Font Family of Legend Text.

Default: “Trebuchet MS, Helvetica, sans-serif”
Example: “arial” , “tahoma”, “verdana” ..

var  chart =  new  CanvasJS.Chart("container",
{
 .
 .
 legend:{
  fontFamily: "tahoma",
 },

 .
 .
});
chart.render();