After 11:59 p.m. EDT on July 15, 2009 (10:59 p.m. CDT Mexico City local time), you will need to apply for a Temporary Resident Visa by sending an application to the Embassy of Canada in Mexico City.
If you need to travel within the week and have already bought your airline ticket, download the Emergency Processing Request Form from the Embassy’s website and include it on top of your application for a visa.
Please check the Embassy’s website for information on how to apply.