op: you haven't told us whether or not you are interested in visiting only guangzhou, or if you also need to stop by bangkok, hong kong, and/or maui during the process.
if the latter, please repost with more details.
otherwise, i suggest you wait till 1 month (or maybe 6 weeks) before your trip and call around 6 travel agents, using both can and hkg as destinations, and preferably nyc as an origin, in addition to phl.
the rationale behind selecting multiple agents is to cover the whole spectrum of airlines that serve your desired market(s): e.g. nw, dl, cz, ca, tg, ac, ua, oz, ke, mu, jl, nh, ac (most of these serve hkg, but not can). in other words, look for chinese, japanese, and korean TAs (plus big outfits like gateway).