Integration is the principle underlying the Canadian corporate-personal tax system: income earned through a corporation and then distributed to an individual shareholder should bear approximately the same total tax as if the individual had earned it directly. The corporate tax paid and the personal tax on the later dividend are designed to add up to roughly the individual's personal rate.
Integration is the reason an owner-manager's choice between salary and dividends is rarely a large tax win in either direction — the system is built to reach a similar destination either way. In practice integration is imperfect, and the small gaps it leaves, together with the side-effects of each route (CPP, RRSP room, deductibility, administration), are where remuneration planning actually happens. Mechanisms such as the dividend tax credit, the gross-up, and the refundable dividend tax on hand exist to make integration work.