Why couldn't one gun simply be configured as the 'master'? That one would control camera movement while the other would be confined to shooting within your current vantage point?
An alternative, assuming both 'guns' have two buttons easily assessable while playing, would be to have a toggle button along with the trigger. Clicking the toggle would have it take over as your camera.
Probably the easiest solution would be to simply move one of your guns offscreen at that point, it would automatically take over as camera, and basically start moving you in your intended direction.. That would be the most realistic I would think.
There are lots of possibilities.