Republican Party will not be unified if an establishment candidate is brokered at the convention.
The base will not accept it, not even to stop Hillary.
It is the Establishments turn to hold their nose and vote for the grassroots nominee.
I think the base will accept the result of the brokered convention (when no candidate has a majority on the first ballot) only if the resulting nominee is Trump or Cruz. Cruz being the best option, because unlike Trump, he can unite the party against Hillary and won’t hurt down ticket candidates,