It's a different bread, basically? It's one of those classic food rivalries, most ppl prefer one or the other.

New York-style bagels are soft, chewy and doughy. Montreal-style bagels, on the other hand, are smaller, denser and sweeter. Both are boiled before they are baked, to create the thick, shiny, chewy exterior, but the water used in each city is a critical distinction. New Yorkers swear it’s the NYC water that makes their bagels so good and impossible to imitate in any other city. Montreal bagels are boiled in water that has been sweetened with honey — a defining characteristic of this style.

http://m.huffpost.com/us/entry/montreal-bagels_n_5247880.html

I disagree with them about not putting cream cheese, most Montrealers might add cream cheese but they are just as delicious with just butter.

More information than you wanted, probably. :)