I leave it completely up to Viggo Mortensen to decide which team he would like to support. If he is a Montreal Canadians fan, then it is entirely appropriate that he wore one of their jersey's under his armor throughout the filming of the Lord of the Rings movies. I fail to see why this would be an issue.
Viggo Mortensen supports the Montreal Canadiens as a great fan since the 1970s. He grew up watching soccer, and when he moved to New York City, he found a great love for hockey. He says he loves the team and the excitement of the games. He indicates that he also loves the camaraderie and spirit exhibited by the other fans of the team.
No, he should not have supported a different team because we all should support the teams we like. Who are we to say that his team is not as good as any of the others. He may have a special connection to his favorite NHL team, and we should support his decision to do so.
Honestly, I don't think anyone who was looking under his armor cared what T-shirt he wore. Mortensen is so hunky and so powerful on-screen that we should forgive him his quirks. Although, if he wants to change it up, I am willing to send him a Philadelphia Eagles shirt for variety.