Considering all the number of branches possible when starting ME3, are there any endings that are unattainable based on your imported saved game? That is, is it possible to eliminate one or more of the new endings based on your previous actions?
Only one choice from ME2 matters somewhat and that's whether you destroyed the Collector Base or not. What matters most is your Effective Military Strength in ME3 and of course your final choice.
In other words your ME1/ME2 decisions won't cause you to miss any endings (just a few slight variations).