How will this work?

You need to Upgrade your gpu if you want to play on max settings. That is definitely a gpu bottleneck. I would go atleast 7850/660. But If you have the budget might as well go with 7950/670.

Should run games just fine, but seems a little pricey.

The components you list only come to $556:

PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: Intel Core i5-3570K 3.4GHz Quad-Core Processor ($169.99 @ Microcenter)
Memory: Corsair 8GB (2 x 4GB) DDR3-1600 Memory ($37.99 @ Newegg)
Storage: Seagate Barracuda 2TB 3.5" 7200RPM Internal Hard Drive ($89.99 @ Amazon)
Video Card: Sapphire Radeon HD 6870 1GB Video Card ($163.98 @ SuperBiiz)
Power Supply: XFX 550W 80 PLUS Bronze Certified ATX12V / EPS12V Power Supply ($59.99 @ Newegg)
Total: $521.94
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-01-06 21:14 EST-0500)

-Wolf sends

well $606 canadian and i forgot to mention this is a prebuilt pc

also if a desktop comes with intel hd 4000 could i put my own 6870

Even at $606 that still leaves $374 for the case, motherboard, optical drive and operating system. I suppose, $60 for the case, $120 for the motherboard, $20 for the optical drive and $100 for the OS, that leaves around $75 as a builder's fee... Not that unreasonable,

If it's prebuilt from a big name like Dell, ASUS, IBuyPower, etc... then I still think it's over-priced, but if a friend is building it for you, it's not unreasonable. If this is something you've found on the equivalent of E-Bay or Craigslist, run away!

-Wolf sends

Edit: Yes, if your system comes with integrated Intel (or NVidia or AMD) graphics, you can still add a discrete graphics card.

ok so i will build one but ill have someone do it for me the last guy didn't adjust the system bios

right now i have a 6870 and a xfx 550w what other parts will be compatible or wok well without bottle necking it?