A few years(10+) ago I did something similar with a gateway application. I conected 2 modems and a diginet to the application thus using the combined bandwidth via the single gateway. I think the application was wingate or osmething, not sure if it's still around.
The concept it that we want to combine the line speed and dial one DSL account.
Both routers are setup in bridged mode (PPPoE) and we dial our own internet accounts.
I was under the impression that you can just merge the two using a PPPoE server on FreeBSD and then than machine can be setup to load share the bandwidth?
Well, why would an ISP allow you to use the same account on 2 lines at the same time? It does not make business sense as they would loose out. People would all just share the same account then and the ISP's would have the same (if not more clients) but a lot less accounts.
It would be cheap enough if you obtained 2 local only accounts and then used them together, or perhaps one account for international and one for local, then just configure your routing to use the appropriate router for international and for local.