There is no difference in meaning. に might sound a bit classical.
As in the dictionary I linked below, に is often used in set phrases in modern Japanese, so it's hard to say 気象庁の発表によるに, for instance.
It may be the right moment to ask about difference between になる and となる. As of now they seem to be interchangeable to me, except for "become someone/something"in which case it seems to always be になる, like in 「ああ、僕もポケモンになりたい。」
There is no difference in meaning. に might sound a bit classical.
As in the dictionary I linked below, に is often used in set phrases in modern Japanese, so it's hard to say 気象庁の発表によるに, for instance.
It may be the right moment to ask about difference between になる and となる. As of now they seem to be interchangeable to me, except for "become someone/something"in which case it seems to always be になる, like in 「ああ、僕もポケモンになりたい。」
It's said that となる focuses more on the result of the change and になる is on the process of the change, and となる sounds more classical/formal, but, yes, they are interchangeable in most cases.
The reason と can't be used in your example sentence is not because what he wants to become is ポケモン but because -tai form is used there.
e.g.
○彼は苦学の末医者となった。
○ゲームの世界で僕は最強のポケモンとなった。
×将来医者となりたい。