The first 2 A340s for AC, numbers 981 and 982 (this latter is now operating for BWIA), were to the initial A340 spec with a 257 tonne maximum take-off weight. Subsequent aircraft, numbers 901-910, were to the uprated standard with a 275 tonne limit.

The additional weight can be a benefit in several ways; more fuel for more range, or more payload, passengers or cargo. Or a combination of the two. The engines are the same so it will be the landing gear and other things that are beefed-up.

Vancouver to Sydney (and Toronto to Hong Kong) nonstop with full payloads was the aim of the A340-500/600s, which latter seem to be no longer coming into the AC fleet, and there aren't enough -500s expected to do both daily.