Just prior to going to school for Aircraft Maintenance at Centenial College in Toronto, and well before joining the Toronto Police Service, I was employed by Hudson general Aviation at CYYZ as a ramp rat. We serviced Canada 3000, and they routinely flew 757's to EGCC and EGPF non-stop. Also saw on two occasions their A319 fly cargo only to EGCC. So I say it can be done.
Also, Air Transat, Royal Airlines, Odyssey International and even British Airways used to fly the 757's across the Atlantic, Non stop from EGCC, EGKK and EGLL to CYYZ.