Lock Maestri has agreed to make the switch to Stade Marcel-Deflandre on a deal that will run until 2022.
The second-row will join a La Rochelle side that are third in the Top 14 table, just two points better off than his current employers, when his contract expires next June.
Toulouse also revealed that they have been unable to agree terms with fly-half Doussain.
The 26-year-old has been linked with a move to Top 14 leaders Lyon.
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