I was pleasantly surprised Sunday afternoon to see an AC 777 arriving YEG ex YYZ (ac 127 inbound/154 outbound to YYZ). Given A/Cs usually uses a319/a320/e190 on most routes into YEG (other than daily 767 service to LHR), any thoughts on what would prompt them to use this big of a bird into YEG? Extra demand? Filling in hours? Special cargo requirements? Further investigation revealed that AC used a 777 as well on 3/4/12.