http://metronews.ca/news/toronto/88083/ ... ed-by-opp/
http://www.thestar.com/news/ontario/200 ... _over.html
Joining the force doesn't give you a free pass, if anything... your driving is even more scrutinized.
Every jurisdiction has what's called 'conflicts court' set up for these types of matters. On those specific court dates, they bring an out-of-town prosecutor in as well as justice of the peace, so that there are no possible conflicts of interest. While many conflict matters deal with officers who have been charged, it can also be from local lawyers, politicians, members of the judiciary, court staff, etc.
Just like anyone else out there, no one is above the law. In fact, investigating officers are usually MORE intensely scrutinized when investigating another officer for an offence. Usually higher up ranking officers oversee the investigations, especially if accidents were involved, so as to ensure no favourable treatments are given. Its not a very pleasant day in court either, since colleagues are called upon to testify against other officers on their force. Still, it has to be done. That's why the higher ups keep a watchful eye on the matters to ensure its properly handled.
So, while the potential for favourable treatment is obviously possible (in discretionary matters), usually the officer IS charged so as to make the public feel better (even where a private citizen might not otherwise have been so charged). Plus, prosecutors are a lot less likely to offer deals to officers so as to not look like they are favouring them.