Arsenal wants to see him in Brazil? If this is the case, this transfer won't be completed until the final week of the transfer window because River and Cruzeiro don't play their Round of 16 matches until late July. They play at River on July 23 and in Brazil on July 30. If Arsenal doesn't already know if they want him or not, I doubt this will happen at all.
I think they mean at the Copa America. Either way you'd want a player like this signed before they hit the big time in one of these tournaments.