For me bringing back old show that been off the air for ever almost never work so while there plenty of shows that if I could go back in time and prevent them from being canceled I would love to like firefly but it way past the time that it could come back and be the same.
Therefore I stick with shows that have only recently been canceled that I wish they would of been allowed to finish
1) WestWorld - It seem not many people agree with me on this but I enjoyed season 4 and I wish they would be allowed to do season 5 which was always intended to be the final.
2) Raised by Wolves - I really enjoyed season 2 and really wish it was allowed to continue. My guess it was super expensive show to produce which led to it being canceled but I enjoyed it.