I was concerned about accuracy too. I recently did another quiz on jetpunk which claimed that Sweden had more islands than any other country in the World. That was probably wrong as well but it's noteworthy that Sweden doesn't appear on this quiz at all.
Good idea for a quiz, but I don't think the information out there is accurate enough. The figure of 180,000 islands for Finland comes from their government who has counted the islands in all of their lakes and rivers in addition to the islands in the Baltic sea. There is no equivalent measure for Canada, but given that Canada has many multiple times the number of lakes and rivers that Finland has, it's quite reasonable to assume the the number of islands in Canada will be significantly higher.
For example, eastern Georgian Bay alone has 30,000 islands. That's a subsection of a subsection of a single (albeit large) lake.
For example, eastern Georgian Bay alone has 30,000 islands. That's a subsection of a subsection of a single (albeit large) lake.