On further reflection the best lens for architecture is probably a reasonably wide shift lens, but they are very expensive and you can, as a second best, do perspective correction in PS. I mainly use 28mm and 35mm lenses for the purpose. It is also useful to have access to a medium telephoto for picking out detail on buildings and I use a 75-150mm zoom for that. There's a few architectural images on my Flickr site (below) and I normally specify the lens used.

With regard to film based street photography you want a reasonably large depth of field combined with a wide maximum aperture! Too short a lens and the subjects can look distorted. I feel that a good compromise would be something like an f2 35mm, but failing that any 35mm.

My 35mm film cameras are Pentax, I don't know if there are equivalent Canon lenses available.

Hope this helps