You can rip existing subs from DVDs with SubRip via OCR (optical character recognition). After it's done you can edit the subs with Subtitle Workshop.

But, first of all, I believe it's already been done by someone else. The very same Japanese Blu-ray with English subs added. Is this all that you wanted to do now? Because syncing the laserdisc audio would be probably much more useful. In case the LD Cantonese audio is really that much better. But, you have to rip the audio from LD together with the video then and be aware of all the frame differences and do the syncing (strictly cutting and pasting) according to those differences.