I have found canvas on Foamcore, will lead to problems, in that it's very easy to dimple it and once dimpled, the print is ruined. I am assuming that you are not putting the finals behind glass. I would instead recommend gatorboard. Considerably stronger, less warp, (which will also happen with larger canvas pieces, 30 x 45 or larger.
As for Qimage, I agree it's a very good program once you figure out the interface. However it won't fix the registration problems on canvas as that is a physical issue with the printer's feed. Epson has finally admitted this at least with their canvas and recommends a print feed adjustment of +50 for canvas. Epson 9800, 9880 and 9600. It's not as big an issue on the 24" printers, but still happens to some degree.
Next time you make a print, say a 24 x 36, where the 24" is the on the running length of the canvas. Check your print's final size, I will be surprised if it's not short of 24 but fine on the 36", since 36" was printed on the width of the canvas. I don't see how Qimage can fix this as it's can't control the physical output of the printer. Also, it's my understanding that Qimage is still using the Epson driver behind it's interface, as it's not a true RIP like Image Print.
Paul Caldwell