So I just found that someone on Reddit browsing through the Gw2.dat amnaged to find and stitch together a complete map of the world of Tyria from an in-game globe . The results show us that the supercontinent of Tyria and Elona are actually a tiny tiny part of a much larger landmass, as is Cantha! This map, while interesting, isn't much use to this project at the moment because there are a couple of inconsistencies with the current map of Tyria (unless this map is from wayyy before GW1, because Orr is whole and Giant's basin is totally different), and we couldn't turn it into a map like auserator's because it doesn't tell us anything about the terrain types of the rest of the world.
Also in the .dat, however, is a second image, which appears to be a compressed and edited version of Jenosavel's map over at Guru, put in-game and made canon. This is a lot more useful since it is more or less consistent with our current map of GW2 (although Jenosavel's version is of Tyria circa GW1, this ANet-edited version shows Orr to be risen), and shows the terrain type of the remainder of the Tyria-Elona supercontinent.
So although this one is inconsistent with the globe we have, it is better than the picture we currently have (perhaps it represents the world as currently thought to exist by the denizens of Tyria? Suppose we would have to see it in-game to find out), this second map can be used to build a more complete picture of Tyria, and get a more accurate representation of the distance between Cantha and Elona, until we know more about the first map, at least.