Its true that Canadian theaters at that time had the right to censor films themselves, but this lost cut thing is all in your mind. For starters, the nature of canadian censorship didn't add things to the films--as if some theater in a backwater town in northern ontario, for example, could request copies of the original negatives from Lucasfilm and re-construct scenes. What they did is literally take a pair of scissors and cut out the "dirty' frames. For example, the moment of impact of Luke's hand being lopped off might have been cut--you see Darth swing and then Luke is screaming with his hand already missing. This is the type of stuff that happened. As for the Walker's exploding head, it is doubtful that it was ever filmed, since it would have required complicated special effects and a completed edit. The tauntaun subplot has never been seen, except in brief behind the scenes clips--ask Jambe Davdar, LOL.

Hate to break it to you, but you are imagining this lost cut of Empire. Many people have done similar things with Star Wars as well, and it stems from reading comics, novels, etc, the imagination of little boys living in 1980, and thiry years of time passing.