Was this a legitamite DUI? (in Canada..)?

I don't think that this was legitimate, but he can't do anything about it because he plead guilty. After all, how were the police to prove that he hadn't had the drinks after entering his apartment? Unless someone at the party reported him drunk, the cops would have had nothing to substantiate the charges, and they likely would have been dropped. Your boyfriend also has the right to refuse a breathalizer.