I really cannot recomend Curitiba, I was there in October last year, it is nothing special, you can use it as a stopping off point to visit the spectacular area of Paranaqua on the coast which is a beautiful train journey through the forest. We did this but I have to say Curitiba was a total dissapointment.
Better opt for the amazing falls of Iguacu on the border with Argentina and Paraquay, You will be amazed.