Cantu, outfielder Shaun Cumberland, and cash were sent to the Reds for left-handed pitcher Brian Shackelford, right-hander Calvin Medlock and a player to be named.
"Jorge expressed his displeasure with being here," said Andrew Friedman, executive vice president of baseball operation. "He's been in this organization for a long time and has accomplished a lot of great things. We got to the point in 2007 where other guys started to emerge and take those at-bats. He was outwardly frustrated by that, and obviously, we don't want somebody here who doesn't want to be here. And so we have been exploring things with him for quite awhile. Something emerged today and I think it will be good for both sides."
Cantu, 25, was the Rays' starting second baseman in 2005 and the team MVP after hitting .286 with 28 home runs and 117 RBIs.
Cantu suffered a fractured left foot in 2006 and played in just 107 games, hitting .249 with 14 home runs and 62 RBIs. B.J. Upton won the starting second base job in the spring, and Cantu was optioned to Triple-A Durham. He was recalled from Durham on April 24, when third baseman Akinori Iwamura went on the disabled list.
Cantu hit .277 with no home runs and 25 RBIs in 25 games with the Rays before getting optioned back to Durham on July 20. Cantu was hitting .303 with one home run and 10 RBIs in 23 games there.
Shackelford, 30, compiled a 2-0 record and a 4.11 ERA in 63 Major League appearances (all in relief) with the Reds over the 2005 and 2006 seasons. He was 0-5 with one save and 4.96 ERA in 41 appearances with Triple-A Louisville this season. Shackelford was originally drafted by the Royals in 1998 as an outfielder, but was converted to pitcher in 2002.
Medlock, 24, has a career Minor League record of 29-15 and a 3.24 ERA in 164 games (41 starts) since he was drafted by the Reds in the 39th round of the 2003 First-Year Player Draft. He was a combined 4-3 this season at Louisville and Double-A Chattanooga while striking out 76 batters in 63 2/3 innings and walking 19.
Shackelford and Medlock will both go to Durham.
"We're going to use both of them out of the bullpen at Durham, and we feel like it adds to the options we have internally," Friedman said.
Bill Chastain is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.