hi,
for all i know, canadian and australian tax forms are only relevant to people from those countries or for companies with a permanent establishment within those countries.
Anyway, apple withholds 20% tax for your sales in japan (that's the default rate), but, depending on your country, you can reduce this rate (in the best case to 0%) by sending in the japanese tax form 3, as described in the itc faq. but it's optional for european developers.
don't know if there's more to that or any "hidden" benefits. i'm not a lawyer or anything like that, so ... yeah!