Hopefully, someone can address this question as it relates specifically to the area that is now Toronto, but in the meantime there are good answers about Canada in general and the US War of Independence (by /u/enygma9753 ) and about English-speaking parts of Canada and the US War of Independence (by /u/Irishfafnir ).
Note that York (as Toronto was first called) was not established until 1793 and that, although there had been a French fort there in the 1750s, it seems that there was not much European settlement there again until after the American Revolution, in the 1780s.