Pesos (MXN) or credit cards are the only way to pay for the things you are going to buy in Manzanillo. The Mexican government has ordered that US or Canadian currency cannot be used or exchanged in Mexico in general, though there are very few places that can or will do this for you. These are: INTERCAM, which is on Blvd. de la Madrid almost opposite the Fiesta Mexicana Hotel and Banco Azteca which is in the Elektra shop opposite the Comercial Mexicana and Plaza Manzanllo shopping mall.
Banks will exchange a limited amount daily, only at certain times of the day (usually a $400 limit). It is much better to leave US or Canadian dollars at home and use your ATM cards at the bank machines available at banks, shopping centres or some convenience stores. By doing this you will get a much better exchange rate.
Note also that the Mexican peso and the Canadian and US dollar all have the same symbol – $. when Mexicans refer to dollars, they are, almost exclusively, referring to US dollars.
It would be likely impossible to cash a traveler’s cheque other than perhaps in a large hotel where you are a guest.
Most visitors come with some Mexican pesos and then use the ATMs to get more as well as using credit cards for purchases in stores. The American Express card is becoming more commonly accepted but many restaurants find the commissions charged by Amex not worth maintaining that option for clients.
In many establishments, they accept only cash. In some cases, you’ll see a credit card sticker on the door but they are not accepting cards. Better to ask up front.