Google was the defendant in this case, so they had little choice but to go to court. Let alone the consequences to their Canadian business, US and Canadian courts cooperate in enforcing judgements, so they couldn't ignore it regardless. (Of course they are choosing to appeal, which is optional but obviously a good idea given the pain this precedent could cause.)
Ah, right you are. Google was a non-party, but was named and served:
"Non-parties affected by Mareva injunctions are not normally before the Court, because applications of that kind are brought without notice. Google was named in this application, served with materials, and attended the hearing."
So the rest of the comment stands, but you are correct that they were not a defendant.
