Argentina shouldn't have a problem fielding a B team. Not sure how popular it would be among Argentine fans tho.
I have mixed feelings thou. These kind of events help to develop the sport if all the people involved are serious about it and the level is bound to be competitive from all parties at one point. You need to have some sort of plan about when the teams' skills will converge, not necessarily to make the weaker team beat the stronger one, but at least to give them a run for their money.
If your plan is for Brazil to become competitive to, say Canada, in 20 years, then i think it might be counterproductive to include them. Getting your team beaten 80-90 to nil for 15 years would destroy moral and any potential popularity of the sport in that country.