I suggest you read through both sets of documentation and see which features most closely match your requirements:
http://docs.particular.net/nservicebus/sagas-in-nservicebus
https://dotnet.github.io/orleans/Documentation/Introduction.html
Vra
I Just watched the video of how Orleans was used to build Halo 4's Distributed cloud services
Oplossing
I suggest you read through both sets of documentation and see which features most closely match your requirements:
http://docs.particular.net/nservicebus/sagas-in-nservicebus
https://dotnet.github.io/orleans/Documentation/Introduction.html
Ander wenke
After going through Richard's course in the Pluralsight, I think that both overlap in functionalities. In my understanding, the grains are virtual, single threaded and live in a distributed environment like cloud.