easter weekend - what's open?
Yes, most restaurants are open on Good Friday. Yes, reservations are essential for Easter brunch.
The easiest way to see which places are open is to go to Opentable.com which is a reservations website used by most of the nicer restaurants in the Chicago area (and many other U.S. cities). You can enter the date and time you're interested in, and it will show you which of the 400+ participating restaurants in the area have availability. They also have a page listing special arrangements for Easter brunch.