As someone who grew up in Montreal, and moved to Silicon Valley, one of the appeals of SV is the weather. Montreal winters are long, cold, and dark. These are not conditions everyone wants to live in. Additionally, the Office De La Langue Francaise will make the life of any English company a nightmare. To top it all off, taxes in Quebec are absurdly high (especially considering the quality of social services). So while Montreal is a great city, I think it would be a poor choice for a YC office.