Do we need a Mexico transit visa?

Hi i'm a Canadian citizen currently staying with my newly married wife from the city of Weifang, China. (Weifang does not belong to Beijing for for Visa exceptions...) but Beijjing is the area of Visa jurisdiction for Weifang city aprox. one hour flight south east of Beijinig. We are planing a honey moon trip to Costa Rica.
Seems to be too involved and a "rained on vacation ordeal" for us to get "Schengen" Visas + the astronomical prices of flights through those southern routes of the Pacific rim countries. USA is out as far as we are concerned. Canada flights are cheaper but too long and also requires a "transit visa for my wife" The best we found so far would be a flight itinerary with a 7:30hrs stop in the Belair Airport Mexico to board our direct f;ight to Costa Rica from there. Could you please advise us with what's required of us to achieve our Vacation plan. Many thanks.
Richard and Xueqiang.