By Allison Lampert, Promit Mukherjee and Rajesh Kumar Singh MONTREAL (Reuters) -Hundreds of thousands of Air Canada passengers were grounded at the height of summer travel season on Monday amid a standoff between striking cabin crews and a government board that said the stoppage was unlawful.

Cancellations of Air Canada flights continued across Saskatchewan on Sunday, as the airline announced it will not be resuming operations yet after its flight attendant union vowed to disobey a back-to-work order.