The Feds brought in a series of new legislation, aimed at curbing money laundrying, which, among other things, empowered Canada Customs to make seizures of money until the person proves legitimacy. The implimentation has been a bit rough as new procedures often are. I hope your experience wasn't too difficult and I'm glad you finally found a car. Congratulations!!!
The principle concept behind the new legislation is large cash transactions must be declared, following the lead of similar legislation in the Excited States where it's proved somewhat effective. After all, if you're making legitimate purchases, you will be able to substantiate where you obtained the money and provide a traceable paper trail. If you're attempting to launder money by purchasing hard assets and re-selling them, it'll make things more difficult.
Another popular way to launder money, by the way, is through casinos. If you've got lots of bucks that you can't justify legally, why not risk it all at the casino? Any winnings are instantly legitimized.
Strangely enough, the chief critics to this new legislation is...... lawyers! They claim being forced to declare large cash transactions will interfere with their lawyer/client privacy privelege. I guess the cash provided by unscrupulous clients is more important than any concepts of law and order.