This topic has come up before. There's no explanation other than GM sets its pricing for each market, as it deems appropriate. However there have been instances where some OEM options are far cheaper in Canada, compared to what US buyers have to pay (when you factor in the exchange rate) AND the overall car cost in Canadian dollars is far less than what they pay in the States given that same exchange rate differential. So regardless of the paint colour pricing differences, we're still fortunate to pay what we do for a C8 in Canada.
It's this exchange rate difference that has GM pounce on people selling their C8's in Canada (flipping them for a profit, before a year and 12,000 km) especially if the C8 makes its way down to the States where the GM warranty is still honoured...and the US Chev dealers get ++ unhappy with the sales they lose to "less expensive" Canadian cars. Or so the story goes...
And then we have the European/Japanese/Australian markets. Have you looked at their C8 prices?? They make the US prices look like an absolute bargain which in turn further emphasizes how good we have it in Canada. But shhhhhhhush; don't pass along these comments to GM.