I asked the CFC the same question awhile back, and they said I would need to inform them of the sellers info, even if it wasn't registered, for me to be able to register it. I said, does this not put the seller in a position of being charged for not having registered it previously? They said it was not up to them, as inforcement was done by the RCMP. When I pushed them as to whether the RCMP would be informed by the CFC, if such a transfer were to occur, they would not confirm or deny, that they would. It sounds a little funny to me. I think the seller would be taking a bit of a chance myself.
It would be great if there was no problem, as I'm sure there are a few good deals to be had on unregistered guns, as the owners might be a wee bit concerned of having them. Chances are they don't have a POL or a PAL either...