It seems strange that YOW, which has become quite a large operation since I was young, has still not managed to maintain a route to the European mainland. Only a daily to LHR exists. (I realize there are probably some charters.)
I would suggest that the demand is there. KLM tried it for a while to AMS, but the Canadian Government was requiring them to make a stop in I think Halifax in order to have rights to the route. That restriction made it undesirable for those originating in Ottawa, and there wasn't enought compensating demand from the Maritimes, so KLM cancelled it. I believe they were doing thrice weekly?
It seems to me that if KLM thought there was potentially enough demand YOW-AMS (government intervention not withstanding), then there would be certainly enough demand for the two powerhouse European hubs: FRA, CDG, would there not?
Is Ottawa still putting this one-stop requirement on any airline that applies?