Some historians believe that Grant's victory at Vicksburg was more critical than the Union victory at Gettysburg (perhaps Grant felt the same based on what he wrote in his memoirs). The loss of Vicksburg did give the Union control over the Mississippi and severed Confederate supply lines, effectively splitting the South geographically. Manpower and resources were certainly on the side of the North. I believe that Lee opted for a strategy where a major Union loss would energize those in the North who wanted to end the war - and this is why he was aggressive (some would say he took too many risks). Longstreet appears to have favored a defensive war - choosing the ground upon which to fight and forcing the North to come to them (while minimizing the South's losses in manpower). It's only an opinion, but I don't believe either strategy would have resulted in a different outcome.