We were in Rio for Carnaval with Celebrity in 2004, there was no mention of it in the brochure etc, but everyone had a ticket and transportation to the Sambadromo to see Carnaval on one of the nights in port, it was amazing, this was not offered as an excursion, just included.
Call Royal Caribbean direct, this is too important to mis.
No, there are no shore excursions etc to see the carnival. Beleive the tickets are around £250pp which you need to arrange yourself.
Royal Caribbean, Celebrity and Azamara will not offer Carnaval tickets, even for purchase as a shore excursion.
Check with Celebrity as I went on a cruise with them which included tickets to the Carnival as part and parcel of the cruise. Excellent..