I would give the new player complete control of the entire Commonwealth.
This gives him 3 pools of money to play with, one completely on land, one completely at sea and one that is the most influential with some choices.
It also gives him complete overview of the entire board, as everyone’s moves directly impact his gameplay.
If you have a competent player doing the United States’ moves, he can help ‘dictate’ the new-comers actions by his own moves, as India/ANZAC largely move based on American aggression.
There aren’t so many units for him to toy with, but he still feels top shelf because his units are all over the board. There’s no complex naval maneuvering like that between the USA & Japan, there’s no massive calculation of large armies like in Russia, there’s no tight economic playing and strategic allocation like that involved with Germany. There’s no need for rapid expansion across the entire board like Japan.
It is hands down the best nation for a newcomer to play.