Not sure about LGW or STN but it definitely routed YYZ-EXT-BHX-YYZ 2002-2005 when I was working at BHX, operated on the A310. Crew change was at BHX. Shame there were no 5th freedom rights EXT-BHX!
CP Air, Wardair, Worldways, Nationair Air Transat and flyglobespan between them served just about every UK regional to YYZ (YHZ for globespan) over the years.