Let me preface my comments by saying I haven't shot hi-def yet, but I've been reading a lot of reviews about the camcorders you mentioned. All 3 are good professional camcorders, but the general consensus is that the Canon XH-A1 will be a bit sharper, and can work under slightly lower light than the Sonys you mentioned. Of the 3, the Sony V1U is the only one that can shoot in progressive mode, which can be helpful if doing post production effects like compositing, freeze-frame, or slow motion (your boyfriend can explain that for you). Also, the V1U has HDMI output, which might be useful in the future, when more compact HDMI recording equipment becomes available (to give better image quality). The Sony A1U only has 1 image sensor (the other 2 camcorders have 3 each), so the A1U color won't be quite as accurate. But then, the A1U costs significantly less.
 Bottom line, for documentary work, the Canon A1 is probably the best choice; but for special effects and compatibility with possible fututre recording methods, the Sony V1U is the way to go.
Good luck!
Ken Hull