Hi Baladina.
The easy answer is that GWT can do anything that JavaScript can do. You would write your GWT apps in
Java, and then use GWT's JavaScript Native Interface (JSNI) to have the Java code interact with JavaScript code. JSNI is used in GWT for those times when you need to interact directly with the browser's JS interface.
As for building a GWT version of Google Maps... yes, you can do that. I am presently working on a GWT widget caller ViewportViewer that works just like Google Maps, including panning, zooming, etc. I started it just for fun a week or so ago. I will likely post the code to my
GWT Sandbox site in the next week or two as-is. If I ever finish it, I will add it to the
GWT Widget Library project.