They've published the program guide now.
Looks like the reason that 2015 and 2016 Volts get the same incentive is that it maxes out at 30% of MSRP.
They appear to have capped the incentive based on the price listed at gm.ca ($39,590), which is actually inclusive of freight, A/C tax, and a $500 credit.
Calculating the way they say they're supposed to, based solely on MSRP exclusive of options, taxes, PDI and freight, the incentive should actually be $11,517 instead of $11,877 ($360 less).
For now we'll call that close enough for government work. It's possible the incentive will be reduced by $360 in the future, after they correct the calculation.