Since the game was released in 2005 without native network support, "online play" is achieved through emulation netplay PCSX2 & Parsec : The most common method. Players run the game on the PCSX2 Emulator
That said, the success of Hi-Fi Rush (a stylish action game with beat ‘em up DNA) proves there’s an audience. Fans continue to petition via Change.org and social media. Until then, the methods outlined above remain your only route.