I think in SignalR 2.0 you can take a look at Introduction to Scaleout in SignalR
.
I have not tested it, but the docs report that for example Microsoft.AspNet.SignalR.SqlServer
will handle load balancing for you using SQL server.
Ref: http://www.asp.net/signalr/overview/signalr-20/performance-and-scaling/scaleout-in-signalr
EDIT
Currently I'm using in production the REDIS backplane and it's simply great, simple to setup and inject in your code https://learn.microsoft.com/en-us/aspnet/signalr/overview/performance/scaleout-with-redis