The most-used exemption is the protection of personal privacy. It's a mandatory exemption. Another mandatory exemption is information provided in confidence by other governments. Then there are injury test exemptions such as injury to federal-provincial relations, injury to international relations or the defence of Canada, injury to the commercial interests of corporations that provide information to the Government of Canada. There are exemptions for cabinet confidences, to maintain cabinet secrecy, to protect solicitor-client privilege, and on the internal deliberative process of government--that is the advice giving, the recommendation making, the negotiation of contracts, and all the negotiation process.
I don't know if I've hit all of them. The investigative process is another one.