There may be other issues too, the more current you drain, the more stressed the power supply will become. If you over stress it far enough, it will blow up or shut down, but before it reaches that state, typically things like noise and ripple will increase, regulation will suffer, and there is a real chance you may damage the cameras.
I would assume the maximum current one of these cameras is likely to draw, will exceed 1 Amp, so worst case scenario is that two will exceed 2A, at which point we may start to see some irreplaceable magic smoke emerge from either the power supply, the cameras or possibly both.
I wouldn't be too keen on conducting the experiment.
If you do decide to try, then you might need to think about some smart power management, for example, don't allow both cameras to zoom at the same time, avoid the use of flash if possible and so forth.
This sort of trick allows large servers to run lots of hard disk, with theoretically under rated power supplies by ensuring only one of them starts up at any given time, since startup current is largest power demand of a hard disk. Once all of the drives are spinning, their current demands are more modest. The same *may* be true of canon cameras...
