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.

Default: Automatically calculated based on the chart size.
Example: 100, 150, 200 etc.

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

 .
 .
});
chart.render();