BC's budget is balanced.

And that is even with a smaller GDP than Alberta, not even per capita but on a TOTAL basis, plus with  a larger population, and enjoying a small fraction of the resource royalty revenue that Alberta enjoys. From Stats Can - In 2015 - Alberta GDP - $325 Billion, BC - $250 Billion. Even with a 2016 10% contraction in Alberta (which did not happen) , and 10% growth in BC (which also did not happen) Alberta's GDP  would still be far ahead 

Gee, I wonder where the main problem is - revenue, or spending?

Freeze public service wages. Long term, until they fall to national averages. Hardly a severe hardship. And then implement a sales tax, or raise personal taxes to balance the budget. Bank every penny of royalties. Every single penny. All services paid for by taxpayers. 100%.

And in less than 5 years, even without an oil boom, the economy in Alberta would again be by far the healthiest in Canada, if not North America. Sustainably.