One way might be Cypress FX2LP (pushing it) - had experience and the processor does not get in the way of the USB bulk transfers. But limited peripherals (I2C CAN controller is a bit mucky).
I do not know of a USB peripheral chip that can pass-through the bulk transfer data (on EP1 for example) to something like a DMA channel.
dsPIC are nice but they do not seem to have the parts.
Any recommendations?
TIA, Bill
PS The prcoessor does not have a lot to do, just looking after some set-up and then setting up the bulk transfer.