Not sure about Toronto, but there are a lot of places like that on the BC side. I don't know if it's true or not, but I heard once that leading up to the handoff of Hong Kong from Britain to China there was a lot of immigration to Canada, due to their easier process than that of the US. It could also just be an Asian neighborhood like you'll find in pretty much every major city.
That was one of the major events, but in general there has been a steady trickle of immigrants from Japan and China to American and Canadian west coast settlements for the past 150 years or so. As with most diasporas, the way it usually works is that the first people come there because it's cheaper and/or because there's work available, and then once they establish a local community, more immigrants start coming there preferentially because they have friends and family, because there are services available in their language etc.
In BC, Richmond in particular has been a recipient of many of those immigrants from Hong Kong, which is why its population is still majority ethnic Chinese, and even many official signs are bilingual.
