There will be plenty of time to position yourself for the long term once the S&P investment grade upgrade starts to make a real impact on the Brazilian economy. However the chances of hot money sloshing in today are pretty high, with articles such as this one linked here predicting 25% index gains for 2008 fuelling the sheep money fire (remember the ADRs traded in New York yesterday but the Brazilian markets were closed for May Day).
ERJ: the Embraer ADR. This one has lagged the market somewhat this year, despite being a great Brazilian success story and an order book stacked up in the billions of dollars.
VIV: Mobile phone play Vivo jumped 6.2% yesterday, but there's plenty more where that came from.
CIG: Cemig is a Brazilian cement play that popped 2% yesterday, but it still under its 52 wk highs. At $21 now, if this breaks $23 it'll be off to the races. Cement stocks become much less boring when they make you a heap of profit.
ITU: Banco Itau got a big pop on strong volume yesterday on the investment grade news, and will be one of the first in line to receive hot money when Sao Paolo opens tomorrow.
GGB: Gerdau Steel has resisted all downgrades on its climb to its current all time high. With a PE of 11.5X right now, there's more in the tank now that Brazil is "officially a serious country"*.
Again, don't be afraid to take a short term profit on GGB, but be thinking about a longer term position afterwards.
So there are six ways to play the investment grade party. You'll notice that PBR and RIO aren't on the list. This because they're already 'world class' investment risks and won't be first in line to get "the pop" from this news. Another way to play Brazil is the useful ETF play, EWZ.
I hope this little overview helps in its own small way. However I'm sure you'll need to do more DD on any or all of these before making a good investment decision.
UPDATE: It's been pointed out to me that CIG (Cemig) is not a cement play, in fact it's a Brazil energy play. Quite right too, and thank you "chinstrap" for point that out. A mistake on my part, and I'll blame writing late at night for it. Any way around, a basic error. Sorry dudes...will try harder next time. And as a little autoflagellation I won't correct the original text (which was corrected on seeking alpha, by the way).
*Charles de Gaulle will be turning in his grave