Is the word mercados the same in Brazilian and European Portuguese?

No

Differences in Pronunciation and Usage

• Pronunciation: In Brazilian Portuguese, the "s" at the end of "mercados" is typically pronounced as a soft /s/ (or sometimes /z/ depending on the regional accent, though /s/ is standard for this spelling). In Continental Portuguese, the "s" is pronounced as a "sh" sound (/ʃ/). Additionally, Portuguese speakers tend to reduce unstressed vowels much more heavily than Brazilians.
• Usage: In Brazil, "mercado" is a generic, everyday term used to refer to any place where one buys food, including large supermarkets or small local grocery stores. In Portugal, the word "mercado" is more specific, usually referring to a traditional municipal market or an open-air street market. For modern, large-scale grocery shopping, a Portuguese person would more naturally use "supermercado," and for a small local shop, they would use "mercearia."

Brazilian Portuguese Examples

1. Vou ao mercado comprar pão. (I'm going to the market to buy bread.)
2. Os mercados estão muito cheios hoje. (The markets are very full today.)
3. Preciso fazer uma lista para o mercado. (I need to make a list for the market.)
4. Existem muitos mercados bons no meu bairro. (There are many good markets in my neighborhood.)
5. O preço nos mercados subiu muito. (Prices in the markets went up a lot.)

Continental Portuguese Examples

1. Vou ao supermercado comprar pão. (I'm going to the supermarket to buy bread.)
2. Os supermercados estão muito cheios hoje. (The supermarkets are very full today.)
3. Preciso fazer uma lista para o supermercado. (I need to make a list for the supermarket.)
4. Existem muitas mercearias boas no meu bairro. (There are many good grocery stores in my neighborhood.)
5. Os preços nos supermercados subiram muito. (Prices in the supermarkets went up a lot.)