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If you're looking to trade Pokemon from a 4th gen game to the 6th gen, you'll need to have at least one of the 5th gen games (Black/Black 2/White/White 2) as well.
From Soul Silver to one of the 5th gen games, you'll need to use Poke Transfer (info on how you can do that right here), and then from there, you can use the Poke Transporter to move your Pokemon to Pokemon Bank, which can then be added to your Y version (info on that right here).