That's an interesting and potentially complicated question. The issues are decided by the interpretation of Section 22(1) to 22(6) as well as the transition rules of Section 24 of the 2002 Ontario Limitations Act (or Bill 213).
As you can see (as per Sec.22.6), business contracts are placed in a separate category from agreements that are normally regulated by the Ontario Consumer Reporting Act.
Initially, there was a lot of discussion and even confusion that occurred between lawyers as to whether or not business contracts in Ontario could be based on extra-provincial laws and thus be allowed to defeat or modify the purpose of the Act which came into effect on Jan. 1, 2004.
The probable interpretation is that for consumer loan agreements, contract law cannot supercede statute law. And so for such debts, the 2 year rule of Section 5 of the Act must apply.
You can see one of a multitude of legal glosses/discussions about this below.
http://www.osler.com/resources.aspx?id=8290
Ray