The photo was taken at the Oscarsborg Fortress. I really don't think it's a fake gun, but I have no idea from which period it is. It looks pre-WWII, but it could also be something the Germans dragged with them from France or Belgium or some other occupied country. It might even be a Norwegian gun. I have no idea. But it seems a few parts are missing.
Most likely it's last usage was as a parade piece. I can't imagine why the white wall tires would be there otherwise.
The carriage is different from the Bofors gun, and the barrel seems shorter. I think this is a field gun, not an AT gun.
looks like a japper feild gun ..whitewalls were only tire that fit the rim at last replacement...prolly
Perhaps not even the rims are original, the whitewalls are probably there just because it was placed outside the commandants resident. Nothing like a field gun or two to fresh up your garden. Isn't Tony active around here anymore?