If the fit is good on the old counter, you could use it to make a template.
Make the template while the old counter is still in place with posterboard and mark the wall as a reference point. Remove the old top and when you install the new one, lay the template on the new counter and align it with the marks on the wall.
Just plan first that what type of design of your kitchen sink and than make a rough template of it than you are easily able to measuring and cutting the hole for the kitchen sink.
Kitchen Sink
Linear Mode
