Boeing can go against the Airbus battle forward as it combines with a Bombardier C series on its wing.
The Airbus-Bombardier consortium does pose new problems for Boeing in the new world order of things. What Boeing can be doing is thinking way out of the box in a counter move. Give Embraer a big corporate hug. Boeing could form an alliance with Embraer with selected airplane types in the market place.
When Boeing talks to a potential customer relating to a fleet renewal order it could by agreement allow Embraer a share at the sales table as a "partner". The alliance would have conditions of course allowing both corporations autonomy much like an airline code share compact that exists today.
In this arrangement Boeing makes a 787-737 deal with a customer but allows an Embraer offer in on the talks only for regional aircraft. If Embraer goes it alone it would not be eligible for any Boeing sweeteners surrounding a potential deal. If Embraer has established a sales lead where bigger aircraft could be included with its regional Embraer order offer, then Boeing would be included for offering anything larger the Embraer's current line of aircraft.
The details of an alliance would fill reams of paper bundles within-the-making, but the legal dance would maintain corporate autonomy and allow each builder to operate in its own realm of airplane making.
Embraer should align with Boeing as Airbus will now make Boeing pay in areas where it does not even make an airplane for commercial sale or operation.
Additionally Embraer will have to battle Airbus sponsored programs alone. Simple as it seems, it is a complex arrangement for either maker which will enable both to efficiently negotiate with different customers' operational needs throughout the regional and intercontinental spaces each maker services.