Can my Ontario corporation do business in other provinces?

Yes, an Ontario corporation can carry on business in other Canadian provinces, but it may need to register as an extra-provincial corporation in each province where it does so. Most provinces and territories require out-of-province corporations to register before they "carry on business" there, though each jurisdiction defines that threshold slightly differently.

Generally, having a physical office, employees, or ongoing commercial contracts in another province is enough to trigger the registration requirement. A one-time sale to a customer in another province usually is not. The registration process is similar across provinces: you file a certified copy of your Ontario articles, pay a registration fee, and appoint a local registered address for service.

Each province where you register will also have its own annual reporting or filing requirements. Missing those can put your corporation in bad standing in that province, which could affect your ability to enforce contracts there or bid on government work.

For businesses that plan to operate seriously in multiple provinces from the start, incorporating federally under the Canada Business Corporations Act can be more efficient because federal corporations have the right to operate in every province without separate provincial registration (though as noted, Ontario still requires extra-provincial registration even for CBCA corporations).