Brancher can mean "to hit on someone" but it is not necessarily flirting, maybe just trying to engage in an unsolicited conversation with someone.

Brancher quelqu’un definitely has a seduction connotation to it, so your proposition (c) is almost correct. You can omit the "walking up to someone" part though, as you could very well "brancher quelqu’un" by message or eye contact.

More generally, "être branché par quelque chose" means to be attracted / looking forward to do something, as in "Ça me brancherait bien d’aller au ciné ce soir".

Whatever the context, it is considered familiar language that may not be appropriated to any situation.