I just checked your ad and saw that you were asking $3500, so I'm gonna re-enact what happened and you tell me if I'm right.
He gives you some reason/sob story why he has to or will send you a check for twice the amount, you keep half and he gets your truck, or he's a really nice guy and lets you keep a little more and return the remainder to him with the truck. Only after this all went down did you realize that it was a scam and you're boned.
Other thought is, if he's supposedly in canada he pays you extra for shipping, maybe a little extra for your trouble.
Now I'm really curious about what actually happened!