the stock nav screen is a very good composite screen, you'd have a hard time finding something to replace it that's better as a direct replacement. the stock screen uses an RGB interface which is common on factory screens of this size, but not aftermarket.
now if by "better" you mean higher resolution & able to take a regular vga pc input & with a touchscreen, then the problem becomes how to display the OE RGB signal on the replacement screen. there are RGB converters, but the issue there is that nissan uses a funky dual sync RGB interface, I'm trying to find a suitable RGB interface that will allow you to display the stock RGB feed on a vga monitor. if that happens, THEN the stock screen could be replaced with a vga screen & you'd be able to switch sources, from stock tech display & then at the push of a button switch to a pc display, but honestly this is not a huge priority to me so I have not put huge effort into finding this solution, but am discussing & exploring this possibility...
there's aguy from this thread
http://www.mp3car.com/vbulletin/worklogs/127015-2007-fx35-carputer.html who is suposed to be sending me one interface to try, but last I heard he hasn't sent it yet.... when I do have some more time I'll extend my search for suitable interfaces to try, but the dual sync issue is a stumbling spot for sure...
& oh yeah, the CAN buss has nothing to do with the RGB display, ther is no CAN communication in this screen interface at all...