I wouldn't say Braga would be a terrible loan, 4th in Liga Portugal, won against our CL opponents Sporting today. Bur perhaps not particularly good either. Girona on the other hand is playing in a division ranked lower than the Argentine league so its obviously out of the question.
Not sure its a good idea to bring him to Europe, and just to loan him out a couple of months in another country either. Moving across the world at a young age is difficult as it is, if any loan to Spain or something would be less than a year, its better to just keep him here and evaluate how good he is, than see what best for him in the summer. Thats why I could kind of understand if he stays in River until the summer, but to let him stay the whole year? Makes no sense at all.