Are you doing this as a person or a business? If all of your invoices / payment information are under a business name then I would definitely speak with or even hire a customs broker and see what needs to be done.
If you are going about this as a individual person just make sure you declare everything because you are going to get questioned. Keep all of the receipts and even take printed copies of the deal making communications with you to prove any declared value that you will put.
The most guaranteed way that you can avoid major issues is to just speak with customs people. I know Customs generally is tough to get a hold of by phone but if you live near a small international airport then drive out there and speak to them in person. I know when I lived in Rochester, MN there was a small customs office at the airport and they were easy to speak as long as you could get to them during their hours.
Also choose your port of entry well. You didn't mention which province you are going to but picking a smaller port of entry may be better because that way if you have issues the customs officials won't be less annoyed by any missing or incomplete paper work. Of course this is kind of catch 22 because you could risk going to a big crossing and just get waived through because they are more concerned with the commercial traffic.
However unless there is someone on this site that makes these kinds of purchases regularly speak to the customs office or a customs broker. Think about it; all businesses in Canada that want to buy directly from Wizards of the Coast need to have a customs broker. There is a reason company's hire them and the price isn't that much.
Custom broker fees are not that expensive. The company that I work for bought a $10,000 machine and imported it to Canada. Using the FedEx broker service cost $55 USD. $55 USD on $10 grand; Not that expensive and it can save you a lot of hassle.
[Edited 1 times, lastly by sys41o on September 23, 2013]