I presume there is sort of a market for YYZ as it seems Air India didn't have any issues making the BHX-YYZ leg work. Air Transat operate an A330 on a few occasions so those flights must be getting filled (though I don't see why they wouldn't do it year round, maybe Air Canada could provide that).
If an indian carrier was to return, which one would you hope it'd be? I'm not holding my breath for Air India, especially considering what has happened recently with them having to go back to square one. Jet Airways is a possiblity, and possibly Kingfisher.
Emirates brought in a second daily flight around 2 years after they brought one in at Manchester. They brought in a third daily flight at Manchester just last May, so if they follow the same pattern, we could be looking at it soon. If that was the case, I think they'd start with the A330. If we are looking at the current yields and pax numbers (and whatever else is needed to be looked at), does it warrant another flight?
I hope that when they announce any new routes for the summer timetable, we may be hearing about the Qatar service, as well as any service to ORD.