As it's got a sloping top tube which gives you extra clearance for standover you could comfortably go for the large, but med would also suit.
As biggsy says best to try but if you are set on this particular bike you should be okay. Can't you find a local bike shop which has something similar so you can just see? Hybrids are the most popular bike for city travel so there's plenty of choice and LBSs will have a good selection.
It's also a better bet buying locally as if you have any problems you can just take it back. They also usually offer a free first service if anything needs adjustment which inevitably it does. Id always recommend buying this way especially if you're starting out with bikes.
