RELAX!!!!!!

At the airport, as you come out, turn left. There will be 3 ATM's. Choose one, take out up to your limit at home. Then, if you need more, use an ATM again. No need for USD, or Canadian, they are difficult to exchange and you won't get a good rate.
When at Comercial, Merza or other grocery type stores, use your credit cards, assuming you don't have a foreign transaction fee. If so, use the pesos you got at an ATM.
Unless your home bank has an agreement with a bank here so you won't pay a small fee, it doesn't really matter who's ATM you use. You will get a great rate.
Welcome to Zihua, have a great time, don't sweat the little stuff, and it's all little stuff!