That's right, if you want only one PAC value from all the data, and ergodicity is assumed (PAC value is the same for one cycle, regardless if it is the next cycle or the cycle in the next trial)
Yes, it is Canolty's, but scaled by sqrt(n) / sqrt(power_fa)
where DirectPAC before the scaling is the complex sum of all the vectors in the complex plane A_fa(t)·e^i(phi_p) so its size is [nSignals, nFreqP, nFreqA]