Matri would have the same effect on CL matches as he does in the Serie a. Which means he'll do just fine. Hopefully he gets a more dynamic RWF in support. E only thing that worries me is that he may not be able to cope in the league and Europe simultaneously. So it may not be a bad idea to bringin somebody with a little more experience in that competition. Higuain Matri in our ranks for example wouldn't hurt because I think they'd find a lot of game time in a CL season.
Benzema has become the first choice striker at Real Madrid. What makes you think that Benzema is even a remote possibility? You might as well think of how C.Ronaldo or Messi fits in Juve's team.