MEXICO CITY, (Reuters) - Mexico’s plans to break a 75-year state monopoly on energy could boost flagging growth and double foreign investment, potentially providing the biggest leg-up to its economy since the North American Free Trade Agreement two decades ago. The government is finalizing proposals to lure private investors into the oil, gas and electricity industries in order to boost production and lower energy costs for manufacturers, which are up to twice as high as those paid by U.S. companies. The plan is expected to be unveiled and sent to Congress this week. It is likely to include tweaking articles of the constitution that prohibit private ownership of Mexican oil. The level of access to private firms, including foreign oil majors like BP and Exxon Mobil, will be crucial to the reform’s success.