Yes, the Celtics will beat the Heat in 5. They have Miami's number this year, especially down the stretch. Remember, the Heat have played dreadful competition over the past few weeks, and their reputed hot streak is nothing but fluff.
Needless to say, D-Wade will score at will. That much is known. However, even when Wade scored 44 in his last game against the Celtics, the Heat STILL lost. This Celtics team may be inconsistent, but if there is one thing they are very good at doing, it is stopping teams that have one transcendent superstar. The only player that seems to evade the grip of that dominance is Lebron....the reason being that he is a PLAYMAKER, and not purely a scorer. When Lebron passes well, and the rest of the Cavs shoot well, it is game over.
Miami is not like that at all. They don't have good shooters, and D-Wade is not primarily a playmaker. The celtics should be able to take the series easily. The games won't be easy, but they'll be PERFECT preparation for the ensuing Cavs series in round 2.