A magnet will normally get them off.
Loads of other ways to do it too if you search online.
I bought something a while back and the same thing happened to me. I tried the magnet trick but it wouldn't work on this tag. I ended up using a variety of tools on it, though I wouldn't recommend that in case you damage the shirt. It was a swine to remove.
As you said, there are definitely plenty of ideas online, often with videos.
Failing that, I wonder if the cousin in Canada knows any local shops he uses regularly and who know him who might remove it for him once he's explained the situation?
EDIT: I see New Balance have a store on Robson Street, Vancouver. Maybe they could help? Maybe your cousin could phone them and ask before he takes it in?
I hope you get it sorted, Farman.