Interestingly, Messi and several other older Argentina players will still take part in this year's edition. They're not done yet and are still the favourites, but I'm not so sure I see Argentina retaining their title. Brazil is definitely ahead of Argentina in my opinion, but I think both deserve to be in the final.
To me, Uruguay has a better chance of winning the Copa America than Brazil. Brazil has not been impressive. They're not as consistent as they need to be. Uruguay on the other hand may not be very consistent but they know how to get points from other American teams and they play as a team more than Brazil.
I believe Argentina will retain the trophy. They're the most in-form team in the continent and they have a balanced square, to top that up, they have the Leonel Messi factor.
Messi makes things easier for the team. As long as they're ready to defend well and don't concede unnecessarily, they stand a chance. They also need to be ready to score the chances Messi creates because he's going to create a lot of chances. I'd like Messi to finish up his career with another international trophy.