I would agree that is the most likely which you specify above. It makes sense to but the extra 1 weekly into Heathrow, but the question is why have they not done this already then? Difficult slot time?
Re: the bilateral. It looks like the extra frequencies granted are simply between UK and Sri Lanka, and therefore LGW-YYZ could operate and not affect their allocation of frequencies per the bilateral.
Last point, does the 332 have sufficient legs to do Colombo - Manchester nonstop and if it is to be operated by A330s, where would they come from as they do not have any on order.
8R