While you are not the first person to suggest a hypothetical "partnership" between BBD and ERJ, this is the first time I have come accross this topic on a.net. There are a couple of alternatives one can contemplate [of course, there are many other variations one could consider]:
1. An acquisition of one company by another. A stock-for-stock deal would simply be a "merger", with the target's shareholders receiving ownership in the combined company.
2. Creation of a new company [a joint venture] dedicated to a new 110-130 seat commercial project with investments by both BBD and ERJ á-la CFM [with both GE
and SNECMA as shareholders] or Airbus [both BAE and EADS are shareholders].
Option #1 appears rather unrealistic give the BBD's dreadful corporate governance and control by the Beaudoin/Bombardier families. Also, BBD's stock value is a disaster now and, even in a stock-for-stock deal, BBD's shareholders would obtain a small position in the combined firm.
Option #2 may be a remote possibility, but, what's the incentive for ERJ to do this? While BBD has made a failed effort to enter the 110-130 seat market with the C-Series, ERJ does not appear to be interested in challenging Boeing or Airbus.
So, while one could consider some sort of "partnership" between BBD and ERJ to further consolidation and create some scale and efficiencies in the process, such an arrangement does not appear likely in the near future.
Should Russia liberalize its aerospace company ownership laws [unlikely], perhaps BBD as well as investors from India and China, could invest directly in the RRJ project as a shareholder.
Who knows? Anything is possible.