Poisson Brackets of EM Field

Since I couldn't find any reference on the subject of Poisson bracket formalism of classical field theory, I'm posting a few question here:

A) What are the Poisson brackets of the source-less EM field?
B) Does the law that the Poisson brackets between a dynamical variable and its conjugate momentum equals unity still hold? Is this law gauge invariant?
C) In classical particle mechanics, the definition of Poisson brackets includes a sum over all dynamical variables. Is this sum replaced with an integral over space when talking about EM field? Is there a useful notion of "Poisson bracket density" which excludes the integral?

Thanks