There's no difference in the control systems between the 3A& Bs - only the time vs temperature relationships in the EICAS ITT indications change. This is because of the differing engine internal parts. Operators can strap the EICAS to retain A ratings so the increased thrust & temps of the B are taken as increased time between overhaul.
As stated the N2 is controlled via a mechanical link to a Woodward Governor mechanical fuel control and then the N1 Amplifier takes over to control to fan speed. As you're aware, if you lose either engine (have an N1 decrease of 15% or more) after advancing the throttle to TO power, Automatic Performance Reserve (APR) kicks in (a ground from the N1 Amp to the APR Relay) to give you approximately 2% extra thrust on the remaining engine.
RJ-700 & -900s have FADECs and are powered by what is really a completely different engine.