Hi,
That's good you know they have received it, how long ago was your application transferred to mexico city?
The MP can contact CIC Ottawa and find out the last thing that was done on your file and inputted into the system. Everytime they do anything to your file they need to put it into the computer system so cic Ottawa has access to this and that's what the MP can get. If you have a really good MP sometimes they can contact Mexico City directly if its urgent.
The ARC will be requested after everything else is approved, relationship evidence, criminality, medical interview waived or completed etc. than the ARC will be requested and following that you will get the Passport request.
I know a lady that just did an ARC and hers took only 1 month and 3 days to approve, instead of the average 2 months. so that's a good sign!!