I'm surprised that LGW will be one of the first routes, especially out of YYC. I assumed the 763s would be used on more "leisure-oriented" flights without J, and the 789s would be used for more "business oriented" flights. YYC-LHR will have both AC and BA next summer, both of which offer big J cabins, strong alliances, lounges, etc (ie. likely more appealing options to business pax).