I believe you will find Canadian drivers much more courteous than U.S. drivers, especially the truck drivers.

Our experience with canadian truck drivers has been extremely positive. On the Trans Canadian Highway where the shoulder is almost as wide as the motor vehicle lane, the truck drivers would pull over to the far left lane to pass us. This was especially noticeable in the plains where wind alway seemed to be a factor. When I asked a trucker why they took the effort when there was plenty of room, he said that they did not want their turbulence to create a dangerous situation for cyclists. We also got friendly beeps from truckers who had passed us several times on the portion of our route between Calgary and Winnipeg.

The point of all this BS is that a flag may be less necessary than in the U.S. Bright clothes and lights during low visibility conditions should be adequate.

This is what happened 99% of the time when truckers had room to pull over. Trans Canadian Highway, just east of Regina.