Hi,
If EF 17-40mm and toki 16-50mm were the same price, I don't know who want to choose toki. If you want to collect "L" lens since you love Canon, or you're very particular about detail in quality or you don't mind the budget to topup, then go for EF 17-40mm. Otherwise, just make use of the lens you have. I too love to have those lenses but money talks.
Best regards,
albert