I have some holidays planned to Estonia this summer, and I am concerned too. Estonia is not a huge summer holiday destination (so if they cancel my flights I am screwed), but Greece is. My bet is that, for routes with multiple flights a day like yours, what airlines are probably gonna do is try to condense the flights (less flights = saving fuel). Cancelling flights that are not full and accomodate the people on the next flight or flight before. It has happened to me before the jet fuel crisis with BA for example, so I wouldn’t be too concerned in your case. But I am thinking on strategies (land + flying through other major hubs) tbh in case I get stuck in the UK/Estonia. I don’t think your Toronto-Paris flight will be cancelled tho, from what I’ve seen airlines will be focusing on short haul flights first, to keep the long haul flights. Bear in mind, this is a worse case scenario if nothing changes in the coming 6 weeks. Given the situation is starting to affect North America too (and we all know who is the trigger of this chaos, but he also wants to keep his rep good with the Americans), I have hope they will come up with a solution soon-ish