The X1900XT would be the better choice for the money.
Why the Connect3D XTX but not XT?http://www.ncix.com/products/index.php?sku=17529&vpn=3056&manufacture=Connect3D
For price/performance for the GF7 series it's the GF7800GT which can be had for less than $400CAD.
The major question is the games you play and the resolution/settings you prefer.
I'd say the XT has a longer lifespan ahead of it, but the GT (not
GTX) has great value going for it for now.
The AIW X1900 is also a nice consideration.