It would matter which can handle more current, i imagine neither are current limited so the 5v will source current to the 3.3v until one gave out
Well, output pins are always current-limited, but you wouldn't want to try connecting 5V high
output to 3.3V low output, or vice versa.
I suspect a better designed [ie, non-lethal] level-shifter will have a 1K series resistor in the data
path.