Republican activists will get the chance to hear three presidential front-runners already running hard in Michigan — Rudy Giuliani, John McCain and Mitt Romney — speak to them this fall on Mackinac Island. The Michigan Republican Party announced Friday that the three have agreed to speak at the party’s biennial Mackinac Republican Leadership Conference to be held Sept. 21-23 at the historic Grand Hotel. Former House Speaker Newt Gingrich, who has said he will wait until this fall before deciding if he’ll run, also will address the conference. “This already impressive list of guests is just the beginning,” state GOP...