Final answer:
Energy advisors must be licensed or registered by NRCan to offer EnerGuide Rating System services, as they are professionals focused on energy conservation in homes.
Step-by-step explanation:
Individuals who must be licensed or registered by Natural Resources Canada (NRCan) to provide EnerGuide Rating System services are Energy advisors. Energy advisors are professionals who measure and analyze the flow of energy in houses and work to ensure an efficient and healthy exchange of air within these spaces. This role is critical as the cost of energy continues to be high, highlighting the importance of energy conservation practices. Homeowners, real estate agents, and HVAC technicians are not required to be licensed by NRCan for offering EnerGuide Rating System services. Energy advisors should understand the science of energy flow and demonstrate an ability to advise on conserving energy, which will likely lead to strong job prospects due to the expected ongoing demand for energy-efficient homes.