British Taste for Mexican Flavours! I'm always surprised (and happily so) when I stumble onto a foreign cusine in a country where I least expect it.  Certainly in London, with its centuries-old ties to India, getting an incredible curry from a street vendor doesn't surprise me. But Mexican food? Discovering good Mexican cusine in England last summer was on par with discovering incredible sushi on a side street in Sao Paulo, Brazil, a few years ago. (After some quick research, I discovered that Brazil has one of the largest Japanese populations outside Japan itself.) Next time you're in London, plan at meal at Wahaca Mexican Market Eating in Covent Garden.  (Covent Garden is a world unto itself.) Of course, leave it to the staidly Brits to anglicize the spelling of Oaxaca!     So once you've supped on your share of fish 'n' chips and bangers and mash, make room for spicy chicken tostadas,  smoky chicken with chipotle sauce,  and lip-smacking quesadillas.  There are three Wahaca eateries in Greater London. I want to know: where's the best Mexican food in Montreal and Toronto?