don't necropost, and it is actually a solid theory; when burned tower burned down, there were Pokemon inside representing the events. those pokemon perished and Ho-oh revived them into the legendary dogs (Raikou, Entei, and Suicune). The represented the lightning that struck the tower, the fire that burned it, and the rain that put it out. The only 3 Pokemon that had this description at the time was Vaporeon, Jolteon, and Flareon. This also makes sense because of similar color schemes. And yes, this is canon, it is from G/S/C, and was revisited in HG/SS.