I assume you are asking for a casting of the characters for a film, so here goes:
GEORGE WASHINGTON. This is a tough one, but I liked Jeff Daniels' previous portrayal, so I'll go with him again. No chance for Kelsey Grammer reprising his role.
MARQUIS DE LAFAYETTE. Lafayette was barely out of his teens during his service to Washington, so a young actor is required. I'll go with the youngish 30 year old Michael Pitt (Boardwalk Empire).
WILLIAM PRESCOTT. There are few portraits of Prescott available, but from one I saw, he reminded me of Aidan Quinn.
JOHN BURGOYNE. The handsome "Gentleman Johnny" was once played by Sir Laurence Olivier, so I'll go with the closest actor to Olivier these days: Kenneth Branagh.
LORD CORNWALLIS. Cornwallis has been portrayed previously by Michael Caine and, more recently, Tom Wilkinson in The Patriot. Wilkinson looks a great deal like Cornwallis, so I believe he should reprise his role.
WILLIAM HOWE. If I was directing a movie, I would have to include my favorite actor, Christopher Walken--my choice for Howe.