Is websaver.ca free to use? If so, how does it work?

Q. How much do the coupons cost?

A. There are no costs associated in ordering coupons; the coupons are free. All you have to do is register and select the coupons you wish to receive and we send them to your mailbox.
Source

I belong to a few sites like this with rewards instead of coupons. Basically, the site runs off from ads (in this case, the coupons are ads). The more you use the site, the more traffic they get. The increased traffic usually allows them to get more sponsors to sign up. It appears this site has a deal that the sponsors help them raise money for charity to make it a win-win for them. The sponsors get new customers and a tax deduction.