The difficulty is that regulations take a long time to promulgate and bring to fruition, and sometimes you really need to be able to adapt to changing circumstances more quickly.
With a guidance, you don't have to go through the Canada Gazette process, which automatically makes it a long process. You can still put your guidance out for comment, get feedback and put it into practice much more quickly. If you could, for example in regulation, have content satisfactory to the minister—that's what the regulation requires—then in guidance define what that satisfactory evidence would look like, it would be easier for people to react and manage.