Brobdingnag doesn't represent a specific nation as Lilliput and Blefuscu do.
Brobdingnag are giants, but they are pointed out as extremely ugly. They have very strict morals, but they don't regard Gulliver as a man really.
Gulliver thought of the Lilliputians as miniature versions of himself, but the Brobdingnagians thought Gulliver was just a toy or tool. The first Brobdingnagian Gulliver met tried to make money off of him.
The Brobdingnagians seem to have very strict morals, because they didn't approve of the English politics and way of life and called them "odious vermin".
Swift depicts the Brobdingnagians as morally sound giants, though they seem to sit upon their high moral ground looking down upon everybody else.