English: Soo-joe (the "oo" sound like in "moon")
Mandarin Chinese (Pinyin): Sūzhōu (the "u" sound like in "flute", the "zh" sound like the "j" in "judge")
Cantonese: Sou-jau (the "ou" sound like in "house")
It's helpful to listen to audio recordings of the pronunciation if you're unsure.