I'm attempting to translate something but this sentence is confusing me.
It's the "お" and "スーシ" that I don't understand. I hope this isn't too dumb of a question..
ツ ≠ シ
ツ ≒ つ and シ ≒ し.
「スーシ」 is how many non-Japanese people pronounce 「すし」.
Jokes aside, the word you saw would probably be 「スーツ」 instead of 「スーシ」.
「スーツ」 means a "suit", the clothes. 「スーシ」 does not exist.
「おニュー」 is a comical way to say "brand-new" or just "new". 「お」 is the honorific prefix for politeness. This is a very exceptional usage of 「お」.
"Is that a brand-new suit by any chance?" would be my translation.
Come back if that does not make sense for the context.
Related: How to understand チラツ