What's the furthest away that your city's skyline can be seen from?
As far as I know, the furthest away that you can see Montreal is from Burlington, Vermont (117.48KM, 73 Miles). It can also be seen from the slightly closer upstate New York.
Photo here:
http://farm3.static.flickr.com/2655/...09679419_o.jpg
(Monctezuma, MtlUrb.com) Taken from above Burlington Vermont.