I think you're thinking of poutine, in which case that isn't mayo. It's cheese curds and then they top it with brown gravy. I only know this because one of the summer hot dog carts downtown started selling the stuff. I couldn't bring myself to try it. I like dipping french fries into tartar sauce sometimes.
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"Returning hate for hate multiplies hate, adding deeper darkness to a night already devoid of stars." - Martin Luther King, Jr.