Originally Posted by sts603

Space may open up. That's a decent possibility.

The time flying via YYZ isn't as great as you think. A YYZ-LHR flight is only 30-40 minutes longer than BOS-LHR. And even consider connecting via ORD - that flight is only 45 minutes longer - and your flight to ORD would be in F vs commuter to YYZ (plus the hassle of dealing with Candaian immigration). I know Chicago seems a long way out of the way but the J experience will be better for you as you will get to enjoy the meal service and then get more sleep. I intentionally backtrack through ORD to get more sleep.

Also, with that many miles - consider F. Though if you are going to do F - the experience on BA may make it worth connecting via YYZ.