Any m4/3 camera will do the trick. If it was me, I would choose one with an articulated LCD (like the G3 or GH2), in case you want low, high or other tricky shooting angles.
You will need a wide lens. The Panasonic 7-14mm is ideal, but expensive. For me, the Olympus 12mm would be the alternative, but maybe not wide enough always. The Olympus 9-18mm is good too, and cheaper than the Panasonic.
For normal zoom, my choice would be the Olympus 14-54mm f/2.8-3.5 II. It's a 4/3 lens, so you would need an adapter, but it will AF on all m4/3 camera. It doesn't have IS on Panasonic bodies though. The second alternative is the Panasonic 14-45mm f/3.5-5.6. It's a stop slower than the Olympus, a little bit less sharp and has built in OIS. It's also considerably cheaper, particularly if you consider that you don't need an adapter.
For architecture, a telephoto lens isn't always necessary, but nice to have sometimes. The Panasonic 100-300mm is the king of the m4/3 territory so far, but it's rather long at 200-600mm eqv. The alternatives from Olympus and Panasonic are ok too, and smaller, shorter and cheaper. Maybe that's good enough for the odd telephoto shot. In that case, I would choose a Panasonic lens for Panasonic camera and Olympus for Olympus to get IS, which is more important for the longer lenses.
Just my 2c