My brother went on vacation one year and met a girl who he later married and sponsored to bring to Canada. It's been 2 years since she has been here, and she's using my brother. She's taking all his money and sending back to her family, and she also treats my brother badly. He claims she loves him and he loves her. But I over heard her telling someone the only reason she married my brother was to come to Canada and after she gets her citizenship and her family over here she's going to leave him, and "take him for everything he's got". Is there a law against this? How can she be stopped?

If your brother is willing and happy "being used", nobody can do anything. This is his business, not yours.

Sadly if your brother does not want to see it or if he does is willing to put up with her, there is little you can do.