It was rumored that Paul Walker already finished most of his part of the shoot and the rest of the gaps was filled by his brother "Cody Walker".
According to London’s Daily MailOnline, a source on the production said although Paul’s character will be retired in F&F 7, Cody “will join the crew. Of course, Cody isn’t a replacement for Paul in any way, but the producers were really grateful that he stepped in to help them finish this last film and Cody is so likeable and charming. It would be a tribute to Paul that Cody carries on the Walker name in the Fast and The Furious movies.”