I just received the photo books I made of my summer trip - four copies. I created the facing pages together, but on separate 12 x 12 templates (which were resized later), so I had a 12 x 24 workspace. Of course, it's possible to create in one large space and then crop into two pages.
The printing company I used, My PicTales, does have the option to upload a two-page spread, and provides templates so you can see what space is "safe" and what will be trimmed. I didn't use this option, but it's available. I did find the uploading process to be a bit frustrating at times, but it worked, eventually, and the printed books were just fine. Hope this helps.