Is there going to be a Sonic Riders 3 and or a Silver the Hedgehog Game?

No. Any Silver The Hedgehog boxart is fanmade and fake.

Especially considering the recent past of Sonic games, a proper Silver The Hedgehog game is highly, highly unlikely. Shadow The Hedgehog is hated by critics and fans alike, sometimes even claiming it to be worse than Sonic '06. If you'll notice, in recent years a selling point for the new Sonic game has typically been "Sonic is the only playable character!" This is in response to games like '06, where the diminishing focus on Sonic and the shoehorning in of other, less-fun-to-play characters was a much-hated aspect. To make a game where you never play as Sonic, but rather a character that has never really been especially popular to begin with, would be a shot in the foot, and SEGA knows this.

But who knows? If the Sonic series becomes more stable with critics and its fanbase, and SEGA truly thinks they can make an enjoyable Sonic experience, there might be a Silver The Hedgehog game sometime in the future. I just wouldn't expect it for another 5 years, at an absolute bare minimum.