There are hundreds of professional associations and occupational licensing authorities that largely operate at the provincial level. That means for an individual wanting to provide their service to a buyer in a province other than where they reside and are regulated, there may be barriers to doing so. These exist in lots of professions. Here in Alberta, we have provincial rules and exemptions surrounding dental hygienists, nurse practitioners, podiatrists, radiologists and things where skills, one would think, are largely portable across the country, yet there is a system imposed on new individuals moving into Alberta to recertify in those professions.
For others, Manitoba stands out as having an explicit restriction on the ability to provide legal services with respect to Manitoba law, if you do not have a physical law office in Manitoba or if you don't predominantly, actively reside and operate as a lawyer within Manitoba. That's another explicit barrier that exists there.