I guess it would depend on what type of investigative work that you want to do. Here in California, there are agencies that are not involved in street patrol such as the Department of Justice, Bureau of Alcoholic Beverage Control, Probation, Parole, etc. There are Federal choices as well such as the FBI, ATF and Secret Service. I'm sure there are equivalents up in Canada. If you want to be a Police Officer, though, you will have to work patrol before becoming a detective (you have to learn how to walk before you run). As far as your degree choice, criminology is a good one, but it would also depend on where you want to work. I always tell prospective candidates to get their degrees in something other than criminal justice, but I'm a street cop who hires street cops.
I would suggest you look at agencies in your area that are not primarily involved in street enforcement and talk to the men and women who work there. I would also suggest looking into an internship with one of those agencies to see how they work and get yourself some exposure to that career field.
Hopefully this helps.
Good luck with your career!