Not sure about the use of 魷 (you) as cuttlefish - I understand cuttlefish to be 墨魚 (mo yu) i.e. inky fish.

Squid on the other hand is seen on menus as 魷魚 (you yu) or 鮮魷 (xian you) i.e. fresh squid.

To extend on your point on which restaurants use which characters; Chinatown restaurants tend to use traditional as most are Cantonese places run by Hong Kong, whilst the non-Cantonese restaurants run by recent mainland Chinese immigrants use simplified.