For authentic Greek Gyros try a place on the Danforth called Messini (I think that's how you spell it). It's not the carboard mystery meat type that's pressed together it's made with real pieces of identifiable meat. Hint ... make sure the owner cuts it or watch them cut it fresh off the spinner so you don't get last night's leftovers. The prices are great, the portions are pretty big and the service is fast and friendly. Also how to tell it's authentic ...there are usually french fries in the pita with the souvlaki meat!!!!
Another place on the Danforth that comes close is Alexandros but again make sure they cut it fresh off of the spinner or you get dry gyros that no amount of tzatziki can fix.