Even when there is, there isn't much (if any) extra legroom, though you are usually guaranteed a window or aisle seat with a free middle.

I wouldn't be too put off by having to fly down the back on a short hop, when the alternative is no better.

One other thing you might like to consider is the traveling times - because Dublin is further west, flights there tend to be very short and arrive very early.

I would always start an eastbound TATL as late as possible to get a good sleep and adapt to jetlag more quickly. In addition, you'll feel much more alert if you transfer before you're jetlagged rather than afterward.

Without being able to say how much more difficult the YYZ transfer might be, the schedule on that route (and potentially the hard product) will be better.