"other countries will happily provide Saudi Arabia with arms if Canada does not."

Only Canada has presented itself to the world as bastion of all that is good and virtuous, with a PR campaign that is constantly looking for any situation to float a good headline.
If the U.S. or any other country sells arms to Saudi Arabia that's of no consequence to Canada. When Canada sells arms to SA it makes a mockery of it's supposed national character. 
The U.S. headlines are of war monger, oppressor and every rotten thing you can come up with to describe us so when we sell arms to SA that's just what we do.  Canada get the favorable headlines and the blood money in a near secret deal.