Yes, terms of service (TOS) are considered contracts. The website or other entity has offered you use of their service in exchange for your adherence to their terms of service. You signify acceptance of the contract by use of the service. Normal contract interpretation, termination, etc will all apply, per the jurisdiction that applies (look for a choice of laws section in the terms of service, then look in your local jurisdiction's laws to see if the choice of laws clause is valid).
There are many exceptions depending on the jurisdiction, for instance if you don't have a French translation, your Candadian TOS may not be valid in Canada, but on the whole, TOS's are considered contracts and probably enforceable.