Particularly in the early '60s, just immediately prior to the advent of women's lib, free love, birth control pills, college radicalism.....
The early 60s would have seen a huge surge in Americans going to unwed mothers' homes in both Mexico and Canada; surely there MUST exist some sociological statistics about this phenomenon, as I'm positive that it isn't mere "Urban Legend" and I'm positive that Canada was popular in MANY American cities, not just Seattle.
The reverse happened tool Girls from Canada came here. There was a big one in Lackawana, NY.