Where to live in Toronto?

Hi to all
I would like to get some advices about where to stay in Toronto. Actually I have been planning to go to Canada in June and July to study and improve my english, but i don't know anything about this country. I just have been in USA some times, but people who has been in Canada told me there is some differences between these two countries, and of course his people and culture.
The institute where i will go is in the downtown, so i need to look for an apartment for one in the same area, to go walking or using the public transportation. Any recommendations?
I imagine there's different kinds of neighborhoods as a good alternative to stay for short terms, for a single guy 36 years old interested in know the city and meet people.

Thanks for your comments!