Although Ubisoft hasn't officially announce Watch Dogs 2 yet, pre-orders for the sequel are now live on GameStop's UK site.
GameStop UK's Watch Dogs 2 pre-orders don't give us any actual information on the game--the release date is TBC, and stock logos are used for box art--but their existence actually tells us a lot. Pre-orders typically follow a major game reveal, as publishers and devs are keen on raking in as much cash as soon as possible to finance further development. When pre-orders open before the reveals, however, that usually means the announcements will follow soon after. Keep in mind Watch Dogs 2 is only listed on the GameStop UK site.
We can then postulate that Ubisoft will unveil Watch Dogs 2 at this year's E3 expo in June, and open up global pre-orders after the official reveal. Ubisoft has already confirmed that Watch Dogs 2 will launch by 2017, and it'll have significant advantages on PC. AMD recently confirmed that Watch Dogs 2 will tap DirectX 12 and be fully optimized for AMD video cards.