Toronto has a lot to offer at any time of the year depending what kind of activity you are looking forward to. Toronto has four distinct seasons and Summers (from late June to August) are the peak tourist season hosting a myriad offestivals, parades and exhibitions. If you are more into outdoor actvities like street festivals, lake's shore, zoo etc then Summers is the perfect season for you, though it gets quite hot and humid. However, being the peak tourist season it gets a bit expensive, so make sure that all booking are done in advance. The weather during September to October is milder and its mid tourist season with beautiful colours and pleasant temperature (gets a bit chilly at night), also not being the peak season means cheap accomodations are available. There are few festivals that take place during this season like the International Film Festival in September. Late November to March is generally not considered a good time to visit, as winter creeps in and temperature drops below zero with fewer actvities to offer. This period is for those who love winter sports and activites, with an added advantage of discounted prices.