Sold Item on Amazon CA. Question about duty

Sold a toy on Amazon Canada (I’m in the US) and I estimated the side at 25 x 13 x 4 but it might be larger as I will have to make a box for it by placing it in polybags, wrapping it in cardboard and placing it again in an outer saet of polybags (since I don’t have any boxes that size). This is what I do on domestic orders for this item.

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It comes out to:

DHL Express International

$31.94 – Tue, Nov 07

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but for 30 x 18 x 6

DHL Express International

$55.77 – Tue, Nov 07

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and quickly up. I like looking for a worst-case scenario in case of bulges etc. PirateShip gives me 30 x 18 x 8 a little cheaper on PMI:

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usps

Priority Mail International

BESTZone 1 • $200 insurance included • Estimated delivery in 6-10 days

Save 6% • Deepest discount available

$52.20 retail

$48.89

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Is that better just to be safe (except without Amazon Buy Shipping Guarantee?

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Also concerned about being charged duty on this going through DHL vs USPS. Which is better. This is a CAD $200 toy (US $144.56).