Little information is available on resistance to extended-spectrum cephalosporins (ESCs) in Enterobacteriaceae from animals in Canada. The study objectives were to determine the frequency of ESC resistance in clinical, cecal, and fecal isolates of Enterobacteriaceae from chickens, dogs, and pigs in Ontario using selective and non-selective methods, and characterize the ESC resistance genes. All isolates were tested for ESC susceptibility and resistant ones were screened for major ESC resistance gene families. Most ESC-resistant isolates were E. coli and blaCMY was the most frequent gene family followed by blaCTX-M for all three animal species. There were high frequencies of intestinal carriage of ESC-resistant Enterobacteriaceae in all three animal species. Whole-genome sequencing of canine and swine CTX-M-positive isolates identified a diversity of sequence types, including human pandemic clones. The blaCTX-M variants found in this study provide evidence supporting horizontal gene transfer of ESC-resistant bacteria and their genes between humans and these animals.