i3-3220 ($132)
seagate 1tb hdd ($70)
LGA 1155 Intel B75 GA-B75M-D3H motherboard ($77)
kingston 2g ram * 2 ($30)
coolermaster 500w psu ($63)
HD6670 gpu ($83)
case ($50)
3 fans ($15)
Total: CAD$520

But if he has a PC already then you can reuse his HDD, case, RAM, maybe mobo & upgrade the other parts

3 fans? and get 8gb ram easy

wat, 4GB is enough

3 fans is enough for good circulation & unless hes using 64bit then 4gb is fine

Edited as your original title said "PC FOR AT LEAST 500 CANADIAN DORRAR"

Thank you.

http://www.logicalincrements.com/

Could cut some corners on mobo/case

doesnt seem so good~ doesnt even list the i3 until > $500

You can also use PC Part Picker in conjunction with the link Plaisi provided. It's very popular, just click 'get started', pretty self explanatory.

Other links that might help you:- Reddit's /r/buildapc & /r/buildapcforme. The resources section on the right-hand side of the subreddit can provide further help too.

Best of luck.

i bought my laptop for ~600€

intel core i5-3210M (2.50ghz X2)
4GB of ram
500GB HDD
AMD Radeon HD 7670M

works like a charm :)