itemMaxWidth: Number

Sets the maximum width of individual legend items after which they get wrapped or clipped depending on whether itemWrap is set to true (default) or false. itemMaxWidth can’t be greater than maxWidth of legend.

var  chart =  new  CanvasJS.Chart("container",
{
 .
 .
legend:{
  itemMaxWidth: 200,
 },

 .
 .
});
chart.render();