ABC confirmed the news.
Canary, known for his dual role of Adam and Stuart Chandler, left the series with Barr's Brooke English in 2010. Meriwether's Ruth Martin was last seen alongside her husband, MacDonnell's character Dr. Joe Martin, attending Tad and Cara's wedding earlier in 2011.
Carol Burnett, Josh Duhamel, Eva La Rue, Thorsten Kaye, Kate Collins, Jennifer Bassey, Melissa Claire Egan and Leven Rambin are also returning to the series.
'All My Children' leaves ABC Sept. 23, but will live on thanks to a new deal between ABC and Prospect Park. The soap opera will transition to an online series and may start as soon as Sept. 26. No official start date has been given.
Speculation on who would remain with the series has run rampant. Susan Lucci, the face of 'All My Children,' has not revealed her plans.