Ubisoft has updated their Watch Dogs Steam page with details on the PC requirements for the game. It’s highly likely this will be the case for the UPlay version as well.
So, interestingly enough, the PC build looks to be quite scalable. Even on recommended, you can run the game in Vista Service Pack 2, granted for the 64 bit version only. Memory requirements are relatively high, between 6 to 8 GB RAM. The game was also made before DirectX 12, so DirectX 11 support is the way to go, with at least 1 GB video RAM. Of course, between these two requirements, it’s highly likely your laptop cannot even run it at all. To cap it off, the game requires 25 GB, so the scalability does not change the fact that this is going to be a huge game, literally and figuratively. You can read the full specs below: