Saint Laurent Boulevard became a boulevard in 1905 and is often referred to as The Main. It serves as the city's physical division of east and west. Street numbers begin at Saint Lawrence and continue outward, with street names being suffixed by Ouest (West) or Est (East), depending on their orientation.
The street is built over a Ley Line, and through generations of settlers and immigrants, it has become a metaphysical dividing line for "us" and "them". This threshold between two mortal worlds has somehow transformed into a nexus for crossing from the never-never as well.
For mortals, the boulevard traditionally divides Montreal by language, ethnicity, and class. Saint Laurent Boulevard was for generations the symbolic dividing line for the city, with the predominantly English-speaking population to the west, French-speaking population to the east, and immigrant communities in between along the Main and Park Avenue. The Main runs through many of Montreal's ethnic communities, a first stop for immigrant communities for over 100 years — initially Jewish, Chinese and Italian, and later Portuguese, Greek, Arab, Haitian and others.
Crossing of the Ley Line is guarded by the Gruff. If you view the city as your home, you need the
Gruff's permission to cross to the other side of the city. If you do not get permission and cross anyway, it has the same effect as crossing a threshold of a home without an invitation. If you get permission, you may may use knowledge of this threshold, and the idiosyncrasies of local magical energies, to your advantage.
Supernatural creatures who consider Montreal their home also live by these rules.
Visitors are not affected one way or another by the Saint Laurent threshold, and do not need permission to cross, but cannot use it's aspect for an advantage. Locals can tap this aspect to create a disadvantage on visitors, if applicable to the situation.
There is an exception to this rule. There are 3 points of "public" crossing for the locals. Consider them are portals of "open invitation". If you cross at these points, then you are not considered 'uninvited':
1) The Entrance Gate in China town2) at the corner of Avenue du Mont-Royal, at the southern border of the Mile End neighborhood.Corner of Saint Laurent Blvd and Avenue du Mont-Royal.
Mile End was also the first important crossroads north of the tollgate located at the city limits of 1792. From the crossroads to the city limits the distance was 0.4 miles (0.64 km). The city limits were located 100 chains (1.25 miles or about 2 km) north of the fortification wall, and intersected Saint Lawrence just south of the current Duluth Avenue.
As early as 1815, there was a Mile End Hotel and tavern, frequented by notables such as Stanley Bagg, an English businessman and landowner
3) Via the Trans Canadian Highway (Autoroute Metropolitaine), or walking underneath the freeway's overpass.The southern section of the boulevard in downtown Montreal and the Plateau is lined with trendy shops and restaurants, and is the site of many street-fairs and festivals. What were once run-down factories have been turned into expensive lofts. Saint Laurent Boulevard is representative of Montreal's shift out of the economic decline in the 1980s and 90s.
Many supernatural creatures have found businesses or locations along the Main that have an affinity with their nature. It's so easy to cross at these points, that the street are amazingly filled with Fae and other creatures. As mortals change the definition of these spaces, it changes the crossing points to the never never. Some creatures get quite annoyed when a storefront is repurposed.

Entrance to Montreal's Chinatown, St. Lawrence at René Lévesque Boulevard.