Fernandita, it is right on the CIC website on the front page, under "I Need To..." and you will see "Check How Long it May Take to Process My Case". Here is the link:
http://www.cic.gc.ca/english/information/times/international/05-fc-spouses.asp
Is Mexico City the only visa office for Mexico? I am not sure. But here is what their timeline is:
Mexico City 6 7 10 15 (basically, most applications are processed between 6-15 months).