"So it's the same storyline," he said. "It's done by the same team, so it's not a separate team in another continent that was (making one of the versions). So, same storyline, same gameplay, all the same mechanics, innovations. All the same missions, if you want, the same world.
"Obviously what's different, is that we're scaling the dynamism and the detail of the city and the gameplay. So it's stuff like the amount of civilians in the street, the amount of cars in the street, the detail in the animation, or how sophisticated some reactions are to some of your actions. So some of those things are scaled down. Obviously the graphics, but that one's obvious."
Guay said he's very happy with what the team has been able to do on the PS3 and Xbox 360, especially in the past six months.
"There were some of our features where it was a challenge to be sure that we had feature parity, especially some of the things that we're doing online," he said. "But at the end of the day we're able to hit that on all the core animations that we're doing in Watch Dogs."
In terms of PlayStation 4 versus Xbox One versions of the game, Guay says they're so similar that he sometimes has to check the controller or the UI to figure out which platform is running the game.
"It pretty much looks alike," he said. "You know, I get fooled. You can't really tell just from the image."
And the PC version scales based on the sort of computer you're running it on, though the team made the decision "not too scale down too much," Guay said.
"I mean you can always say we support a 10-year-old PC and then it's barely playable, but that's ugly," he said. "It's not really what people want to play. We didn't do that. We didn't go there. We said, ‘OK, we advertise that at the recommended setting it's going to be a good experience. It's going to look good, it's not going to look like a 10-year-old game.' So we're not going to support very old PCs. If you have very powerful PCs, then it'll scale up, and it scale up to even higher resolution, obviously, than you can have on PS4 or Xbox One. So you can have, in theory, a version that will look spectacular if you have that big screen, that high resolution capability. The game looks great on PC."
One of the reasons that's true is because development on Watch Dogs actually started for the PC first.
"When we started developing, the PS3 existed, the Xbox 360 existed, and we kind of suspected, maybe, there might be other platforms eventually," he said. "So, because we thought that would happen we chose the PC as our first target to have when we started developing Watch Dogs so that we have the flexibility to adapt to a different platform. So we were able to support 360 and PS3, but we could scale up with other platforms and to other video in the meantime, which we now know is the case. So PC has always been around for us. Sometimes it's a last-minute port of sorts. For us, it's been around since we started."
Development shifted to the next-gen consoles once the PS4 and Xbox One were announced, and then in the last eight months or so a dedicated team returned to the PC to hammer out the final details of that platform's version of the game, he said.
"So we end up having the best of both worlds basically," he said. "We're able to have good usability on PC and on console."