Paul Walker -- Brothers Will Mimick Paul's Voice For 'Fast and Furious 7'

Paul Walker's brothers don't just look like him, they sound like him too ... and TMZ has learned the "Fast and Furious 7" folks will use their voices to help fill out portions of Walker's movie dialogue.

Sources close to the the Walker family tell TMZ ... the production team for "FF7" will try something they have never done before ... merging archival audio of Walker's voice with his brothers' voices to fill in some gaps in the movie.

We're told it will take both brothers, Caleb and Cody, to get everything to match up. Our sources say the production team tested the voice of each brother and learned that certain words sound better coming from one brother, and different ones from the other ... so they will combine them to help make the dialogue work.

Our sources say the men have already started working on production.