I believe your career is limited to certain area in CA firm, but while the whole federal government, not limited to CRA, maybe CBSA, NRC, DFAIT...etc are only some of your possibilities of your career choice.
Once you get into federal government department, you can apply to any possible opening in all federal jobs where outsiders cannot have access to.
Changed your mind?
I totally agree with dkwan. But from my prospective, I only have a college diploma in accounting and have no other experience in Canada. I found myself hard to compete with other candidates in the federal goverment who has a degree. I worry that when I finish my first few month contract with CRA, but can not secure other employment in the goverment sector.
My original thought is to stay in a CA/CGA firm, after a year or so, apply for CRA, since they hire every year in the tax season. Then I would have more experience to look for other jobs in the private sector even I can not secure an employment in federal govement.