The challenge with these is the big firms have the resources and technology but they are usually expensive the smaller firms dont but they are less expensive. Depending on your volume, you should have a direct interface into their ordering system so there are records of every transaction in a common system. A couple of pros that were missed:

-Don't have to deal with staffing issues
-Can handle surges in business

We have not used any firms in Canada so I cant be any help there