The donair is a western version of doner kebab if I'm not mistaken. Mediterranean, gyros, all from the same kind of origin. It all stems from spit cooked meats (lamb, beef, chicken). Thinly shaved slices of seasoned meat.
They're fucking delicious too. Here in Nova Scotia, they've taken ownership of the "donair" because it's now attributed to a sweet sauce that most people get with them (condensed milk, vinegar and garlic) It's literally the selling point for some reason. For me the sauce is nasty and ruins the meat/meal. I never get that crap on one.
Typical toppings are raw onions and raw tomatoes. Cheese has become a huge option and imo rounds it out to perfection. Heartburn City, look out!