As I mentioned, historically, different populations migrate into Canada through different corridors from the United States, largely because different diaspora communities are centralized in different areas in the United States. For example, in places like Minnesota and so on, you have a high degree of Somali and Djiboutians, whereas on the Pacific coast you have a lot of Chinese, Iraqi, Afghan individuals, and so on.
What is unique about the Lacolle situation is that, post-earthquake, Haiti has a significant number of individuals located in Miami and New York City. Plus, the French language draws a lot of the Haitian claimants into Montreal, largely for their children to go to French-speaking primary and secondary schools.