Yeah you will get something more like wide angle to standard lens... It is in fact a 1.6 crop so 27.2- 64mm for the Canon 17-40mm L f4 which is a wonderful lens you will find others like the Sigma to provide good value, but I  know a few have been disappointed when compared to the Canon... So if you can afford the Canon you wont be disappointed.. 

For a wider view on the 1.6 Crop the The Sigma AF 10-20mm f/4-5.6 EX HSM DC is good but a bit slow at the 5.6 end while the Canon retains f4 througout the zoom range ..

Danny O'Byrne  http://www.digitalartzone.co.uk/

"All the technique in the world doesn't compensate for the inability to notice" Eliott Erwitt