The ranking in terms of population (source wikipedia) says that the Catalan Countries would be the fifth State in the USA. Only California, Texas, New York and Florida are above in the ranking. And the next one would be Illinois and Pennsylvania. The ranking in terms of territory or area (source wikipedia) says that the CC are 45th between Massachusetts and Vermont. Of course the CC are a small territory.

So the answer to the question is: NO, Manhattan is not larger than the Catalan Countries.

Manhattan = 1,537,195 people in 33.77 sq mi (22.96 sq mi land + 10.81 sq mi sea)
The Catalan Countries = (but more information in the Catalan version, I think you can understand the basic one) 13,534,721 people in 27,227.92sq mi (only Land)