OS System Choice

I am starting a new project on Nios II that involve porting existing code from an existing Power PC, Nucleus PLUS C++ RTOS embedded controller application.

The project is considering a NiosII dual processor design, using uCLinux on one as the scheduler and server, and the other as a the controller connected to hardware running either MicroC/OS-II or Nucleus PLUS RTOS.

I am trying to decide on the OS for the controller cpu, Nucleus or MicroC/OS-II

What are the main differences or advantages between the systems?

and how much work would be involved in porting to the MicroC/OS-II os?