Mining pools, exchanges and processors have no direct say. All that is needed for the BIP to be merged is agreement among the lead developers. That would be Van der Laan, Gavin Andresen, Jeff Garzik, Gregory Maxwell and Pieter Wuille. Correct me if I missed a name or am in error.
Miners have most of the power.
No.
We do. (assuming you hold any bitcoins)