The "never-ready cases" are only specified to fit the kit lens (EF-S 18-55mm f/3.5-5.6), and won't take anything bigger - so you may get a small prime in them, and just possibly your EF-S 10-20mm f/3.5-4.5, but your (presumably Sigma) 17-70mm is almost certainly too big (and my EF 16-35mm f/2.8L, EF 24-70mm f/2.8L and EF 70-200mm f/2.8L IS lenses are definitely too big!). That, plus the problems Jon talks about means that they can't be recommended. I believe there's an ongoing demand for them in the Japanese market, which is why Canon keep bothering. I'm 99% sure they don't accommodate the grip either.
This thread mentions alternatives - either a Toploader style bag (from Lowepro, Tamrac and probably other manufacturers - all my bags are Lowepro, but that's a personal thing) or a couple of neoprene cases from Zing and Optech.
You can chest carry the Lowepro Toploader / Topload Zoom bags - the bigger Toploaders include a basic chest harness, and you can rig a Vest Harness (or Shoulder Harness) and Deluxe Waistbelt combination to chest carry a Toploader (see here and keep reading to the end of the thread for details of how you do it - I really ought to come up with some pictures, but nobody has asked for them).
David