What is the cannon called in Chinese — 炮 or 砲?
These answers restate the rules implemented by our open-source engine, which follows the WXF laws for movement, checkmate and both repetition rulings: a side that forces a repetition by perpetual check or perpetual chase loses rather than drawing. The chase half has not been validated against the official casebook. Where an answer refers to a specific position, that position lives on the linked reference page, where the build verifies it before publishing.
Direct answer
Both, and both are correct. 砲 carries the stone radical 石, from the trebuchet-style engines that threw rocks; 炮 carries the fire radical 火, from gunpowder artillery. By convention Red writes 炮 and Black 砲, and nothing about play depends on it.
A small piece of history in the character
The older weapon threw stones, and the older character reflects it. The gunpowder cannon came later, and so did 炮. That the piece exists at all is itself a dating clue: the cannon appears in xiangqi around the Song dynasty, which is when artillery became familiar in China.
In notation
Chinese records use whichever character the set uses, and WXF romanisation sidesteps the question entirely with C. So 炮二平五 and 砲二平五 are the same move, written C2=5 either way.
Related questions
Which one is Red's?
By convention Red's cannon is 炮 and Black's is 砲, the same kind of split as 帥/將 for the generals.
How is it pronounced?
pào, for both characters.
.