I am looking for a way to power a camera and a 3.3V, 2W laser (always on) in an OEM application. Which of the two - USB or Firewire – can sustain more power?

The power requirements that you outlined tip the scales in favor of FireWire. USB can only deliver 2W of power but Firewire Cameras, specifically FireWire.b cameras, can deliver a maximum of 25W. Though FireWire.b cables are actually rated to withstand 45W, using the lower value is recommended for safety reasons.