I don't agree Tunisia is a weaker squad. African champs vs. Oceanic champs. Line should be dead even imo, if not in favour to Tunisia.
Tunisia had the better of play against Germany for 75min until that penalty shot. They deserved a lot better scoreline then the 3-0 shown at the end of the game. Also against Argentina they sent out a almost reserve squad and only lost 2-1.
Australia took Argentina to the edge but I think the scoreline is slightly misleading. Argentina had gotten into a comfortable groove with the leads they built up and Australia was able to get back in the match by resorting to 3 at the back. The scoreline could have gone two ways, back to repectable or embarassing. Fortunately for the Aussie's they were able to keep scoring with the desperation tactics.
Bottom line is if both teams come to play (impossible to know exact motivations, lineups) Tunisia would be a slight fav imo. Australia' poor defense is too much to overcome.