I've mostly had good luck from CRC in regards to duty and good shipping times and customer service. I had one warranty item that was dealt with quickly and effectively… they didn't even make me send the wrong part back, as it would have cost both me and them more to ship and process. The express posted me the warranty part, clearly marked "warranty" to avoid any duty issues.
If making a big order (like when I was building the kids' 24" bikes for xmas), I always split the orders since CRC's shipping is free over $100. Smaller orders nearly always go via post rather than courier. Certain large objects like frames and wheelsets may go via courier. So by splitting your order, you limit your exposure of the whole shipment being charged duty or taxed as a "full bike" or if a single item of clothing is included.
I just placed an order yesterday for $200 of mostly parts and spine guards for the kids for park days. I got shipping notice today and it thankfully went via post. we'll see if body armour gets hit for any duty charges. But at $55 cdn for the spine guards, even with duty it: a. beats significantly any other online pricing; and b. gets me youth protection that I couldn't even find at my LBS's. Fingers crossed.