Since everyone knows that one of the main actors of Fast and Furious, Paul Walker (Brian O'Connor), died in a car accident, how would they ever be able to make a 7th Fast and Furious?
They were only halfway through making the movie when he had passed away, (if you don't know what happened, click here) so instead of just cutting him out completely, it is said that he will be completely CGI (Computer Generated Imagery) in the next movie. In order to do this, they have found 4 people who best fit his physique, they will be used for movement and as a base. Paul's face and voice will be completely CGI. Whoever told you that "Justin Bieber will be the next Brian" rumor baloney is wrong, it will still be Paul Walker. It wouldn't make sense either. A 20 year old taking over for a 40 year old? No. Paul Walker will still be in the movie.