It's going to be interesting to see what the best setup ends up being - Gana as the six and Onana box-to-box, Garner behind Onana distributing and playing as a Busquets lite, or Onana in the destroyer role and Garner in the box-to-box role.
All of those options would seem to have advantages and disadvantages. If everyone's healthy, it's possible to see Lampard cycling through those options to give opposing managers selection fits. If Garner proves not to quite be up to speed for the Prem yet, it's easy, but if he is we can give opposing teams a lot of different looks in the middle of the park.