As Danilo said, most of the diving done around the city of Rio de Janeiro is done in the towns of Cabo Frio, Arraial do Cabo and Angra dos Reis. In all of the three the diving is similar. It consists mainly of boat diving to reefs at nearby islands. They are all fairly shallow, mostly less than 10m (30ft).
The water conditions can vary substantially. Most of the dives I've done there had water temperatures slightly less than 20°C (68°F) and visibility at 8m (26ft), but it has been as good as 23°C (72°F) and 15m (50ft) to as bad as 15°C (59°F) and 2m (6ft). In regards to current, I've always found it negligible.
These town are about 150km (93mi) away from the city of Rio.
You can also try diving in the city of Rio de Janeiro itself. It also done from boat at some islands. I've never tried it, though. Additionally, if you have technical dive training, you may consider diving the wreck of the CT Paraíba, which sits at around 55m (180ft) and can be reached by boat from Rio.
In any event, as Danilo said, the best diving in Brazil can be had in the northeast. I have been to Recife and Maceió and they both offer wrecks at varying depths, some big others small and all with an incredible amount of fish life and crystal clear, warm water that rivals that of the Caribbean.
Edit:
Only after submitting my post did I notice the date on the OP. I hope you were planning well in advance.