i traveled with my son when he was 2months old (from Canada to HK).
1) as long as the liquid is for baby use, there's no problem with the custom. but actually there's also hot and cold water on flight.
2) i did bring a little bit 平安藥, just in case.
3) passport is a must. if ONLY you travel with your daughter, a consent letter from your husband may be requested by the canadian custom, as well as the birth certificate.
4) bringing extra (soft) water from HK is a good idea, i didn't do it though. the water here in canada is hard water.