Suncor had looked largely invulnerable to the headwinds facing other Canadian oil producers, chief among them Alberta's mandatory crude-output cuts, because it was able to boost output of higher-value synthetic crude to make up for reductions at other operations. But the company on Wednesday cited the curtailment program as the reason for cutting its production forecast to 780,000 to 790,000 barrels a day from its earlier range of 780,000 to 820,000.The cracks are showing for a few reasons. One is that Alberta's curtailment program was extended for a year in August, forcing Suncor to dial back the production outlook from its oil-sands operations. Also weighing on the forecast was an unplanned outage at Suncor's Hibernia platform off Canada's east coast last quarter.Despite the reduced production pace, Suncor continued to chug along on the financial side.