That's one advantage of having the Olympics during the summer. There's more excess capacity that can be turned on.
Vancouver seemed to cope relatively well. The biggest transport challenge there wasn't public transit, but all the bus transit they had to provide for the athlete's and officials. This had to be a completely separate system, so required huge number of buses and drivers, which they scrounged from all over North America.
With year's of planning, TTC should be able to keep 2-3 years of buses that would have otherwise been disposed of in mothballs, and keep a higher number of driver's available.
2020 would coincide with the planned opening of both the Eglinton/Scarborough LRT and the Sheppard subway (ha,ha .... though perhaps it's the only way it will ever get built ... though they might have to extend it to the Aquatic Centre at UT Scarborough ...
. The TTC would suddenly have significant excess buses and drivers available when these two lines go live ... so they can hold onto them for the games.