"bridge connections" means that traffic seen on one interface, will be repeated on the other. That's not what you want.

In general, there exists technology that will let you "span" (different from "bridge") connections and double the throughput, but usually you span at a layer lower than the IP layer. You can also pull router silliness like sending all even IP destinations out one interface, and all odd out the other, if you're using a kernel that supports it. Can easily be done in Linux; probably slightly harder on Windows (but maybe not much).

There's still the issue that you need to set up redundant DNS for your name (yourgame.yourdomain.com, say) so that different users come in on different interfaces -- and then you might send packets back to them using a different circuit than the packet came in, which may confuse certain draconian cable company routers...

However, a better solution is probably to put different traffic on the different interfaces. If your world has multiple zones, then run half of the zones on one interface, and the other half on the other, for example.