LOL at the $4500 computer. That's crazy. A $2500 (Canadian dollars) PC will give you 90% of the speed of a $4500 PC. OK, maybe if the $4500 needs to include monitor and speakers and printer and mouse and so on, then it may make sense.
The exchange rate is around 83 cents US/Canadian dollar, officially, but computer hardware costs a lot more in Canada than you'd get by converting Newegg USA prices with that exchange rate.
I like jack64's build. Maybe with a Corsair 1000HX PSU, but the Toughpower is good too.
Of course, with that budget I'd use three GTX 285 cards or two GTX 295 cards. In general three GTX 285 cards will beat two GTX 295, even if it's only 3 GPUs against 4, because they have higher clocks and the 4th GPU of the GTX 295 QuadSLI is not used very efficiently.
You could also add a Velociraptor or a SSD.
If you need speakers I'd recommend Logitech Z-5500.
Maybe an Auzentech sound card too.