In all fairness, interact involves fees for the consumer (depending on which bank you are with), and, outside of students who may not be eligible for the, almost everybody has credit cards.
In fact in 2000, Interac Direct Payment surpassed cash as Canadians' preferred method of payment,7 and debit card payments have continued to grow.[1]
Offering credit cards only is a bad choice for a business, since Canadians will be looking to use Interac as well. The entire "debit card" market as Americans understand it doesn't exist in Canada for exactly this reason.
Re: Fees - Many banks now offer no fee debit usage. Such as my credit union - Coast Capital Savings. I haven't paid a surcharge on my debit card use since like 2001.
1. http://www.cba.ca/en/media-room/50-backgrounders-on-banking-...
I don't use cash and haven't for years. I only pay with debit.
The practice of charging $x to use your card (whatever it is) by smaller businesses is actually against their terms of service and you can technically report them.