Let me see... Well, there was this thing in the past, called WW2, it was a WW, because well, Germany for example didn't want France buying Brazillian agricultural products, and sunk Brazillian ships using submarines. Thus making Brazil join the war.

Right now Lula wants to form a coalition with Russia, so what makes you think, in case of war, Brazil would keep selling to the EU? Maybe because USA would threathen Brazil? In that case they would focus on feeding themselves, and not the EU still.

In the entirety of human history, a base war tactic is Siege. What makes you think nobody will try it again?

While Europe has a long coastline, there are only a given number of ports capable of the high thoroughput needed to feed Europe’s population. Blockade those and the entrance to the Baltic and Mediterranean, and most of your work is done. Moreover, in a shooting war, merchant ships from other global regions attempting to supply Europe would be targeted.