The build sheet info I got for mine states a bench seat optional, otherwise came with a bucket seat. Wonder what that bucket would look like? Also states there were 857 of them built. This one looks to still have the original wheels on it, how long has That car been sitting Eh!?
In terms of sales literature the Canadian Pontiac Sedan Deliveries were covered in the 1957 Canadian GMC sales brochures - I can't say for sure but I don't think there typically was much information on them in the car brochures
I have found a few other Canadian GMC brochures and have noticed that
Here's a diagram of a '57 Chevy sedan delivery showing the buckets:
And a page from the '56 Chevy panel brochure (which includes sedan delivery) that shows a bucket seat - not sure if it is the same as what would be in the Pontiac, though.