I knew what you were talking about in your first post, but I wanted to pretend not to understand & see your reaction.
Your choices are simple:
Either pay the extra money, even though you did not agree before hand.
Or ask him to return the money & cancel the deal.
If he tries to keep the money you sent so far, you'd have to contact a lawyer.
Start to gather all the PROOF you have, that he agreed to $3000 Canadian (2000 US)... and that he received money so far.
That is unless you already bought it or whatever...