You're coming to Toronto? It's the end of May and its still freezing here
As for shopping, definitely take a stroll down Bloor Street, the stretch
east ofAvenue/Queen's Park/University Street. All the brand names are there - Vuitton, Chanel, Gucci, Prada, Hermes, Escada... intermingled with the not so brand-names such as Sporting Life, Nike, Gap, Roots and Zara. You'll also find Holt Renfrew on Bloor, which carries a lot of brands along with their own private label.
After Bloor, you might want to check out Yorkville, which is very close to Bloor. It's a small charming area filled with cafes with patios and restaurants, but also has unique little stores from antiques to paperies to candy stores.
For vintage, go to Kensington market. However, the vintage in Toronto is not so recommendable. From my experience, a lot of the stuff is not in good condition, and many stores there try to pass cheap mass-produced clothing as vintage, so be careful
Shopping malls.. all of them are pretty similar as they all carry the same generic brands. So if you've been to one, you've pretty much been to all of them. The closest one downtown would be the Eaton Centre. But trust me, you only need to see one...
And if you have time, check out Queen Street. There's also many stores there that are pretty interesting, especially if you like funky, independent designers.
Enjoy Toronto and have fun shopping!