It Is Pronounced "Tro-PAY": Out-of-universe. Word of God is that his name is pronounced 'MOR-riss', not 'maw-REES'. This is the case in the audiobook. Why Terry didn't just name him "Morris" is anyone's guess.
He didn't name him "Morris" because in British English that's how "Maurice" is pronounced. Not an example
Removed:
He didn't name him "Morris" because in British English that's how "Maurice" is pronounced. Not an example