http://marinebio.org/species.asp?id=190: The gullet of Physeter macrocephalus is the largest among cetaceans; it is in fact the only gullet large enough to swallow a human.
...but that is a whale, not a 'big fish'. It is however, the critter shown in the Bible Stories book, swallowing Jonah. The whale shark, as you point out, couldn't do it due to the narrow esophagus: http://www.oceantoursmexico.com/blog/could-a-whaleshark-swallow-a-human/
Among fish, it seems a very large Great White Shark could potentially swallow a human whole. Of course, surviving in the stomach of any creature for 3 days would be physically impossible.