There are in fact more than 1 domestic configured J (I think 3 to be exact?), under normal schedule, one would be operating the YYZ-YVR flights, another will be doing YYZ-YYC flights while the third one will be doing YYZ-YEG flights. One of those will probably be a purple elvis everyday.
I think it's really stupid that they would use a Club Empress 763 to operate YYZ-YUL and not use it on long hauls instead... more stupid decisions by AC/CP.