Just got this message from AC. I'm coming from central Canada so the issues shouldn't be to bad.
Allowing a free change. Not bad for day of departure.

Tracon your upcoming travel at Vancouver (YVR) may be affected by airport or air traffic control constraints.

Currently, your flight is operating as scheduled, and no action is required.



Want to make a change?

• If you would like to change your travel plans, you can rebook your flight at no cost, subject to availability in the cabin you originally purchased, within 3 days from your scheduled departure. Changes will apply to all customers on this booking.
  
• To make voluntary changes to your itinerary, click the button above, and then select ‘Change my flight.’