Like Father Steve I believe what you are referring to is called balogna in Canada but this is generally sliced quite thin (a millimeter or so).

The only other thing that sounds like it might be it is what we would call a sausage patty – but this has to be cooked and is generally eaten at breakfast with eggs.

>How does luncheon meat differ from spam? Or is spam simply another of those trade names like 'hoover' that have gone generic?

There is a SPAM sold here that sells itself as luncheon meat (competitors to KAM and KLIK). It comes in a rectangular can that you have to open with a twist-key, but that is a solid block of pink meat-like substance. I am still unsure if this is what the Monty Pyton crew were referring in their Spam skit.