Don't exchange at the airport, major rip off!!!!
How long are you coming for? You can use just US in most tourist places. What area will you be visiting?
You can't use Canadian here but can change it to pesos or whatever.
I just used my ATM card or CC when traveling but many people will tell you not to or be careful bc there are many scammers out there and fraudulent charges. Make sure if you do use your ATM to go into the bank to use the ATM, not just standing alone one type things. They are a little safer....