Collection for a company that no longer exists?

I don't know Canadian law and am not sure if our laws apply. However, since they say they have supporting documentation, tell them, "Great! Then run right along and xerox off copies for me and send them down and I will take a look at this." :)

I doubt they really have any documentation and they certainly will not be able to go to a now non-existent OC to get hem.

Did the original lender go out of business or was it bought out?

When lenders go out of business their receivables - the money that is owed to them - is a an asset. They usually get sold (either voluntarily or by a bankruptcy trustee) as part of the winding down process, at least in the US. And many lenders that aren't going out of business sell off their loans. There are even websites where companies go to buy and sell debt. I doubt that whether the original lender is in business or not is relevant to whether the debt is valid and collectible by someone.

Actually it is VERY relevant because generally when a company buys a debt, they get only the basic information in a file and maybe a statement or two. When a debt is disputed, by law the debt purchaser MUST validate the debt by getting paperwork from the original creditor, which would be a bit hard to do if in fact the company is no longer around.