It remains to be seen how much food Brazil and Argentina will now sell to Russia from this point. RB does a good job of explaining past and current situation, but the whole point is that US-Euro sanctions and counter-sanctions by Russia are leading to new global alignments; for example a Russia-China block is being strengthened (Russia will start selling its gas and oil to China instead of Europe) and the EU countries are now complaining that Argentina and Brazil aren't playing nice and will sell directly to Russia. So, let's wait and see how things will change. It's looking much like Germany and other European nations are going to refuse to go along with US sanctions, which are only ruining the fragile European economies.
For one, I'd feel safer as an expat in Argentina knowing that they are aligned with a rival of the US, no matter who that is. Russia, or any country in Eurasia, is too far and probably too uninterested to do anything bad in Argentina, other than act as a counterweight to the US. The US by contrast has begun to harrass expats and others (see FATCA, and what others have said). The US is flat broke, has a phony economy based on usury and on the artificial strength of the dollar, which it is desperately trying to uphold, in part by starting (ineffective) wars around the world, in part now by trying to block the new BRICS fund, in part by harrassing and trying to dispossess those of its citizens who are not politically connected or who speak up (see Snowden). It is furthermore extremely meddlesome to its friends, and aggressive in trying to change local cultures. I think with the discrediting of the US for the past decade in the middle East and elsewhere, countries are noticing it is both aggressive and weak, basically an irrational power not to be taken seriously, but which can still do great damage to others, and are abandoning the sinking ship accordingly.
The economic relationship with Russia is only a part of the policy, I think Argentina's realignment will be much broader, and will be good for both Argentines and expats.
One reason grains aren't going to be the basis of the new relationship with Russia, by the way, is because Russia is one of the largest wheat producers in the world. So RB, your comments are really neither here nor there. We don't know what's going to happen now that sanctions are in place, or how much Brazil, Argentina will sell to Russia.