How about the Swissair codeshares through Zurich?
Zurich airport has an absolutely fantastic kids playroom/nursery with changing stations, microwave, toys for a wide range of kids etc.
9pm-ish out of Toronto so probably not too disruptive with sleep patterns at that end, 6am into Singapore.
Add to that the fact the airport is relatively compact (although the play room is in the Schengen zone so you'd have to go through passport control to get there).
I see the fastest way seems to be Air Canada daytime flight to London picking up the BA flight to Singapore. This doesn't involve a terminal change but would probably be a terrible flight for timings with a baby...