You can't compare UD to Canada period. Its a different market altogether, and the price you see is never the price you pay when you add on exchange, extra shipping, brokerage and duties and extra time it takes.
As with most things, supply and demand dominates price. Prices will fluctuate based on this and constantly. You also have to consider this: if a product wholesales at 80 upon release and retailer A buys 10 boxes while retailer B buys 2 then goes up in price to 100 a box, chances are retailer B will re-buy before retailer A and will have to raise his price to make his profit. You will also see discrepancies because of that as well. Don't discount retailer B because of this however. Customer service, reliability and trust are also valuable in this business and not everyone has these virtues.