Driving days until Canada refer to how many days are left before the group reaches Canada's Border. It varies depending on the current game mode.
Most game modes have the standard 15 driving days. Short Trip to Heck Mode and Quick Death Mode reduce the number of driving days to 9. Meanwhile, Long Winding Road Mode, and Marathon Mode increase the driving days to 25 and 30, respectively. These four are the only game modes that deviate from the usual 15 driving days.
Less driving days means that the game will go by much faster, giving less time to prepare for the final siege and Canada's Border. In contrast, more driving days gives more time to prepare, but the road ends with more zombies at the finale than usual.
Driving days until Canada will not go down if the group is currently walking. However, when close enough to the border, a car is no longer necessary and the party can walk the remaining distance.