There are a good many bags which accommodate an ordinary laptop, but 17.3" is a big laptop, and I don’t know of many bags with pockets that spacious. A possible exception might be the MONO M80. The front pocket is far too small, but it has a rear pocket which is as wide as the bag itself. This is really intended for tucking the shoulder straps into, but could be used for a laptop instead. It has no closure, but is deep enough that this shouldn’t be too much of a problem, especially since it’s on the back. The thinner your laptop is, the more comfortable your carry will be.