Any wideangle will do for landscape/architecture. Personally, I'd go for a 24mm prime (and that's precisely what I did - I don't do landscapes, but I do dabble in non-traditional architecture occasionally - though initially I bought it for a crop body and used it as my main street photography lens, but moving to FF made it less useful in that regard, for me anyway, I much prefer the FoV of a 35mm and/or 50mm lens for street - for 35mm I have a Fuji X100 and for 50mm, I have a Sigma 50mm F1.4).
As far as 24mm lenses go, you prettymuch have five choices - the Sigma 24mm F1.8 (which is the lens I use), the Canon 24mm F2.8, the Canon 24mm F1.4L I and II(the latter being optically superior but far more expensive, both of them being out of your budget range), and of course the Samyang 24mm F1.4, which is optically the best of the bunch, if memory serves, but is only limited to manual focus.
But the Canon 17-40mm F4L is a more versatile lens in terms of focal length... but not aperture.
As for people shots, your 50mm is just fine. Frankly I wouldn't get a longer lens than that, but that's just me.
A 85mm lens would be great for portraits, i.e the Canon 85mm F1.8, or better yet, the Sigma 85mm F1.4. Or the Canon 100mm F2, or the Canon 135mm F2L.
Long story short, I'd recommend a 24mm lens(the Sigma is decent, but not as good as the Samyang which is manual focus, but optically far superior - still, the Sigma is more than adequate, like prettymuch every modern lens out there, especially when talking about primes) and a 85mm lens(if you absolutely must have something a bit longer than your 50mm for portraiture... though since the 85mm has FAR superior looking bokeh, I can sort of see why one would want it, despite it being a bit longer). If you go for the Sigma 24mm F1.8 and the Canon 85mm F1.8, then that should be more or less in your pricerange. The Sigma 85mm F1.4 is superior, but a bit more expensive. If you can squeeze it into your budget, I'd recommend it. They might need calibration (you'll have to send them in with your body for that), but imho it's well worth it.