This is a crop from a hand-held shot taken with an image-stabilized zoom lens at 250mm, sharpened and contrast enhanced in PhotoShop. It's a 747 at 34-36,000 feet. Based on what I could make out of the logo, tail markings, and a ton of research from there, it's a cargo flight owned by CargoLux, the biggest cargo carrier in Europe based in Luxembourg. http://www.cargolux.com/. I'm totally fascinated by aircraft and take every opportunity to catch a shot of a passing flight. SW Ontario, Canada, is one of the busiest air corridors in North America. At any given time (given light and atmospheric conditions conducive to contrails), I can count up to a dozen aircraft in view at most times.
I've attached the full file as well as it's sharper and shows more detail.