Dave, Someone else will come along with some REAL info, but here in the States, I don't think any truck ever had a Fisher Body tag. Maybe a picture of the whole truck would be helpful.
Not that it helps you any but I can make out General Motors of Canada on the second photo, so the vehicle is Canadian origin. Is is a Chev or GMC truck?
Canada may be a different story I would have to say also. However when I've read the comment several times on a variety of posts over the years (and again here on this one) that Fischer had nothing to do with truck parts I question that. A fellow member and myself both have cowls that have the location with 2 screw holes on the lower passenger side cowl where the Body by Fischer tag would be affixed. No evidence that a tag was ever fastened there, just the holes with the reinforcing tab behind. If these are car cowls made by Fischer that we both have on our trucks then at the very least one could say is that Chevrolet made a similar shaped cowl for the trucks as Fischer made for the cars. The other comment I have read multiple times over the years is that trucks were built by what ever parts were lying around at the time (or something similar to that anyway) Could this have been the case by anything manufactured in Canada also? Possible I suppose. You say you came across a cab? Do you have more pictures of it, and is it something that's for sale? David