Toronto loves hockey, and though a second team may take a while to find it's niche, the Leaf overflow would carry them initially. And in a world class city, I can't see corporate sponsors not lining up.
London loves EPl Football. Tottenham, Arsenal, West Ham, Chelsea, Crystal Palace, and Fulham are all in London. Watford is just outside of London. 7 out of 20 teams.
I see no way a second NHL team wouldn't be a huge success in The GTA.
Granted it's not easy, as they'd have to pay off The Leafs.
Local Derby's are sweet. Manchester United v Manchester City, Everton v Liverpool, Celtic v Rangers....
Perhaps it makes too much sense as a sports rivalry to happen...