Exchanging US CASH to Canadian dollars?

Any bank in the country will do this.

Any bank should / will do that, but you might need to be a customer. You can also use major credit cards to purchase things, or with a debit card or credit card and its pin, get CDN$ out of an ATM - and your card issuer will convert to USD on your bill (with maybe a small fee).

i think sometimes airports might do that

for every 1 us follar is 1.26 canadian so 120 is going to be 151 canadian dollars

banks in northern states may do that

I think any bank will do it for you. Not a huge issue. And I'm positive a lot of stores here in Canada will take American money and change it over, so you'll get more money back.