While the MXF format is said to be open source, it is in fact top of the line and so recent as never to have been even conceived of when X3 was on the drawing boards... So you would have to luck out enormously to expect X3 or other amateur editing packages currently available to accept the format. And Canon itself says that is only editable in what are top of the line (and thus very expensive) editing packages:
The Canon XF Codec is currently compatible with leading software programs widely used within the video production and broadcast industries including those available from Adobe, Apple, Avid, and Grass Valley.
That being said, it will film using that codec, in "hot-swappable Compact Flash cards in either 1080/60i/30p/24p or 720/60p/30p/24p ". But to repeat, the MXF format is so far unknown to amateur software packages of which I am aware, and I have no idea when or if Corel might support it...
I guess the moral of the story is that if you buy a professional camera, you need to buy a professional editing package. I imagine that Canon will provide some software, but as usually it will be pretty basic. It might allow conversion to one of the formats recognised/produced by VS, but then again, that would rather defeat the purpose of buying such a camcorder in the first place, wouldn't it?