I can't see much of anything in those pictures.
I can tell you its impossible for it to be a poly 318, as that block is totally different than either the early or late hemi's.
What you have is definitely a Dodge hemi. What size I'm not sure, but if the intake decodes as a '55 its a 241 or 271, the later 315/325's had taller decks and therefore different intakes.
It's possible it was a replacement block, they came unstamped from the factory but were occasionally stamped by dealers or speed shops with their own codes. Or you just may be looking at the tail end of the stamping, which was just a serial number type stamping. It could be that it just happens to be 318. Kind of like how the VIN on my Dart GT ends in 340. Doesn't mean anything, its not a 340 car and that's not how they were designated.
My guess would be that just to the left of the "1-318" you're seeing the is the prefix code. It can be difficult to see with all the accessories attached.
As for it being made in Canada, sure it could have been. There were 3 foundries casting block at the time, one was is Windsor. Again, they weren't different from the other Dodge hemi or poly blocks regardless of what country the foundry was in.