You can now view hundreds of Americas photos from the National Archives online. The images are from the Colonial Office's Photographic Collection and include some of the earliest known photographic depictions of Canada dating back to the 1850s. Some of the images have accompanying background information to give them context, but many do not.
The photographs have been uploaded to Flickr. http://www.flickr.com/photos/nationalarchives/collections/72157630514580494/