Canadian judges can rule whatever they want, it isn't going to make a difference in practice: if Canada or a Canadian entity wants data from an EU company they're going to have to go through the proper channels to do so. Taking shortcuts like this, even with the backing of a judge just isn't going to fly.
Yes. Canada only gets to affect the Canadian subsidiary of OVH. Otherwise they can't do a whole lot. Maybe they can do enough though - maybe they can seize the profits from the subsidiary going to the parent company, which the parent company would want to avoid. They have no direct control though.
If it had been the European one that was the subsidiary, then Canada could order the OVH parent company to order the subsidiary to do things.
A difference could be that Germany might not have such blocking law as France. At least I have never heard of it.