Earlier, we confirmed that Houston's godmother Aretha Franklin would perform, and Gospel singer Marvin Winans will deliver the eulogy.
Both Costner and Davis will speak during the service while Wonder is planning a musical tribute to the late star.
Davis is said to be coping well with the tragedy. A family friend tells People, "Clive has been a complete rock for her family this entire time. He's been with her since the beginning, and he's been everything to them. They're leaning on him for emotional support. He talks to them hourly, and he's a very big part in planning her funeral. They're thanking God for Clive."
In addition to possibly attending, Oprah's OWN will air a two-hour special called, "Remembering Whitney: The Oprah Interview," featuring Houston's controversial 2009 interview and Winfrey's own memories of the late singer.