About from Hong Kong to Mexico by plane?

No... There is currently no direct flight from Hong Kong to Mexico City... So the most direct way would be a connection at North America...
United Airlines operate flights from Hong Kong to San Francisco and San Francisco to Mexico City... And both flights are operated by United Airlines... So it would be much easier to do single airlines connection rather than choosing Cathay Pacific then to connect onto American Airlines flight at Los Angeles...
The flight schedule for United Airlines option is as follow:
UA862 Hong Kong - San Francisco 1145~0850 Daily 744
UA821 San Francisco - Mexico City 1105~1725 Daily 320
And return flight as follow:
UA820 Mexico City - San Francisco 0705~0955 Daily 320
UA869 San Francisco - Hong Kong 1240~1800 Daily 744
The flight time (including transit) is 18hours 40mintues for Hong Kong to Mexico City while return flight on Mexico City to Hong Kong will take 21hours 55minutes...