IIRC Air Canada flies just about every aircraft it has ever owned (including the B747) on the Toronto - Montreal sector (Main maintenance base in YUL, main hub in YYZ). This sector is probably the heaviest domestic sector as well. 310 miles
Swissair (SR not LX) used to fly Geneva - Zurich with their B747s, DC10s and MD11s usually as tag-ends. LX does this occasionally. 143 miles.
And I believe SABENA used to fly between Kinshasa and Brazzaville with their B747s - 16 miles.