Touche...from one of GM's pages:
GM Page about the 3400
They list the displacement as 3350cc. That only calculates out to 204.43 cubic inches. So 205 still seems high, but is much better than the 207.
They also list bore and stroke as 92x84mm, so the volume of the cylinder would be:
pi * bore radius^2 * stroke = 3.14 * 46^2 * 84 * 6 cylinders = 3350395 cubic mm
So there's the proof for the 3350cc.
Bore and stroke in inches is 3.622 x 3.307
Displacement that way calculates out to 34.07 per cylinder, 204.44 total.
So really, it's not quite 205, but it would depend on how accurate 99Alero needs it.
And FYI, a can of pop is .000000000000000375 cubic light years. I just couldn't help myself. :P