They actually used B767-200/300 types for flights to YYC from Mexico City.
One of my visits to YYC during those early days I saw it arrive and park right at the B20 gate. Mexicana also flew here during 2001/2002 summer period using A320's.
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There's a pretty funny picture in the offices of one of the ground handling companies in YYC of about 30 guys pushing out an AeroMexico MD80 by hand - because there was no suitable towbar for that aircraft on-base, and the AA MD80 and NW DC9 (at least, I think NW was flying DC9s into YYC at that point in time... maybe not) towbars apparently didn't work....