1) Simple math. GM sells tons of trucks in California where regulations are set to become stricter.They need as many ZEV credits as possible from Bolt sales to offset. Since 1st year production is expected to be in the 25,000-35,000 range, this doesn't leave much stock for Canada.
2) It's already happening with the 2017 Volt. There's a 2-4 month wait in Quebec at most dealers. Meanwhile, California dealer lots are well stocked. More telling is the $3,000 manufacturer rebate on the Volt which is not available in Canada. Heck, it's not even offered in Michigan. Only residents of the 10 ZEV states are eligible, which is a clear sign that GM is first and foremost angling for regulatory compliance.