From Ottawa on a nonstop to Europe, vs presumably connecting in Toronto onto LH?
I'm scratching my head as to why this is even a debate? Must be a rhetorical question.
Sure, if it's LH F vs AC J, it might make sense, but as a J vs J, I'd avoid the connection, thereby reducing the chances of Murphy's Law being evoked by more than 50%. AC can protect YOW customers in YYZ anyway since it has the second, later departure there.