So a dead whale will accelerate to current speed faster than a dead minnow?
I won't quote them, it's a bit offensive. . My first post in this thread is the physicist answer (er, because I too am a physicist).
To specifically answer your question: Assuming equal streamlining, the minnow will accelerate to current speed faster. Yes, the force of the current is higher on the whale, but the mass of the whale is also larger...in fact more larger than the force is larger...so the whale accelerates less. This is because mass is proportional to volume, drag is only proportional to cross section. Volume goes up faster than cross section.