Uche, 27, who has had a string of injuries through his career, is to finalise a four-year deal with Villarreal. He is away on international duty but on his return will play this season on loan with promoted Granada, the two La Liga sides said.
De Guzman, 23, who has represented Netherlands at youth level, came up through the Feyenoord youth system before joining Mallorca in 2010.
He will sign a five-year contract and be presented to fans on Friday.
Villarreal finished fourth in La Liga last season and have qualified for the group stages of the Champions League where they will meet Bayern Munich, Manchester City and Napoli.
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