YVR-MEX-ZIH is still the way

Dig deeper. It is better to be disappointed now when it is possible to make other arrangements rather than later…

Pets are not accepted in checked baggage at any time (year-round) for flights to/from Huatulco, Ixtapa/Zihuatenejo and Merida

Pets are not accepted from May 15 to October 31 for flights to/from all other locations in Mexico

Mexico City is not included on the AVIH permanent and seasonal restrictions, pets are accepted.

https://www.westjet.com/en-ca/pets#id-91CBBC96F97DE622CE6B5727A9270CA8-tab-1

Airlines may have a maximum number of pets in hold as well as a maximum number of pets in cabin, by seat class. For this reason I reserve my flights as early as is practical.