Gambling is a form of entertainment with a cost, not a way to make money. Decide what that cost is before you start, set a deposit limit at the operator, and treat the limit as the decision rather than something to revisit mid-session.
Warning signs worth taking seriously: chasing losses, gambling with money set aside for something else, hiding how much you play, and feeling that you need to keep going to get even.
ConnexOntario on 1-866-531-2600 is free, confidential and staffed 24 hours a day for anyone in Ontario. Every other province runs its own problem gambling helpline, and the Responsible Gambling Council at responsiblegambling.org lists them alongside its own resources.
Canada has no national self-exclusion register. In Ontario, self-exclusion through OLG and iGaming Ontario covers the registered Ontario sites; elsewhere the provincial lottery corporation runs its own scheme. Offshore operators are connected to none of them, which is one more reason to be careful about where you play.
You can also set deposit limits and take a cooling-off period at most operators directly, usually under account settings.