Just to throw another variant in the mix, if one goes to Nova Scotia, one finds a thing called a "donair" (pronounced doe-NAIR). It looks sorta like a gyro, but it's spiced beef formed into the spit log, not lamb, and the sauce is not yogurt-based, but (I'm not making this up, folks) a mixture of garlic, condensed milk, vinegar, and powdered sugar. Even the locals suggest (only half-joking, as best as I could tell) that
1) Donairs taste better after one has had a few beers first
2) If you get any suace on your shirt, burn it, because you'll never get the smell out.