I actually hear occasional similarities between Japanese and Cantonese. For example: "world" is "世界", "Sai Gai" in Cantonese, and its "Sekai" in Japanese.

Wow, that's a lot closer than the Mandarin Shi Jie. Anyway that's one of those Sino-Japanese words; they're kind of like the English equivalent of French loanwords so there's a whole lot of them. Also I guess I have to take back my "it won't help you with listening" bit if Sino-Japanese words are that close to their Cantonese counterparts.