For that budget I would go with the stuff I listed above, with the 5750. That comes out to $420CAD+shipping.
What PSU does he have? It may need to be replaced to power the new system. If it does, this would be my recommendation. It's the cheapest one I could find that I would trust for that system, taking into account possible future upgrades.
OCZ 550W : $65CAD
Also, on another note, how old is his HDD? If it's about the same age as the rest of his system I would highly recommend that be the next part that is upgraded.