Montreal has a lower cost,
Montreal has a greater abundance of relatively younger providers, and
Montreal has more completely uninhibited providers with a huge variety of service offerings, including fetish.
The likely reason for Montreal being so strong in those areas is that Montreal has a hell of a Farm System
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Personally, when I visit a place, I like to see local providers and eat local cuisine (the gross poutain notwithstanding). I get the feeling that the native Toronto providers are a lot like U.S. providers. They often get into the business at a relatively later age and they really want to be well compensated. So the immigrants often provide better service at a lower cost. No big deal if you are really into Asians - U.S. law enforcement ruined the once vibrant San Francisco Asian sex scene, and Asia itself is a hell of a long plane ride from the U.S.
But if you really want to see top-notch Canadians on your Canadian vacation, and if the three categories I listed where Montreal is the clear winner are of interest to you, I think Montreal is the winner.