In the first place, an EP-3 is not an anti-submarine plane it’s an electronic warfare plane. In the second place, North Korea doesn’t have a submarine that could stagger all the way to the west coast undetected. Since a CP-140 from Comox was involved I suspect it’s a U.S. sub that happened to be passing through the area and they were taking the opportunity for some ASW practice.
Yes, most likely a training/interoperability exercise.
I agree, the participation of the RCAF Aurora might indicate an exercise. Then again, we don’t really know.