I don't think it is as clear-cut as people are making it out to be. To me Ankh-Morpork seems to have some obvious London references, as well as obvious New York references. So I think it's more of an amalgamation of Anglosphere major cities instead of any one thing in particular. Using dollars and pence for currency, sort of covers all of the English speaking countries. There are lots of cities represented in AM, which is why so many people think it sounds like 'their' city. For example, in the forward for the Truth he specifically states that the way that AM worked out its flooding problem was "curiously similar" to the way Seattle, WA worked out its own.
If TP thought there was something funny to reference from Dublin or Toronto, or any other English speaking large city, it's probably in AM somewhere.
The other places in the books are similar too, I don't think any of them are one specific place, but combinations of things that sort of fit together. And some of those places may fit with other places someplace else as well.