We found great prices flying to Mexico City from Toronto. Throughout April and May, prices are good for multiple dates on multiple airlines.
Departing April 5 and returning April 10
$411CAD departing April 5 and returning on April 10. Book this flight directly with American Airlines and ensure the currency is properly set to CAD for accurate Canadian dollar pricing if applicable. This flight does have some connections and it is a little long for Mexico city. On departure you will connect in Dallas, and upon return you have a connection in Dallas and then Orlando. It makes for a longer day of flying, but you can save money.
However, for $472CAD, there is an offer from Aeromexico which takes you to Mexico City and back, direct, without any layovers.
Departing April 16 and returning April 20
AeroMexico outdoes all of the competition again by offering a direct flight for $422CAD. Delta has a similarly priced option, however there will be a connection each way. Optionally, use a site like kayak.com
Tickets are selling out fast for the discounted flights, so you may have to play with the availability calendar to find the date the works for you with this pricing.
It’s hard to find this route for less than $550, and even then it is not as common. Air Canada regularly charges $550+ for this route, with current pricing around $700CAD to $1100CAD