As an ex-pat Englishman I have always said Toh-ron-toh. Those "t's" are there for pronunciation people. Of course, that leds me to another one of my language pet peeves....those that believe "pronounciation" is a word.
Agreed with 'pronounciation' not being a word. I hate that one too. I have to disagree with your first argument though. I am an ex-pat Brit also, but locals have the last say as to how to pronounce the place they live in.
I'd never tell someone from Detroit that it should be De-trois or that Connecticut should drop the second 'c' if they aren't going to acknowledge that it is there.
Teronno is what it is even though foreigners are surprised when they hear Canadians say it.