An A330 to YYZ if it improved OTP even just by quicker loading at both ends.
won't hold my breath!
Hartford is an interesting one. Half way between NYC and BOS more or less. Might pull in a little traffic via Amtrak down from Vermont/Western Massachusetts, and hopefully substantially more up from the fairly sizeable New Haven on the coast (which is where Yale University is located). With an AC codeshare it might be able to offer additional seats to YYZ on non-direct days when BOS capacity is tight and the alternative offered is ORD.