From the conclusion that both programs compute the same result it can be concluded that  the fact that you have made use of a list comprehension has forced  you to make a choice which should not matter, i.e. the order in which to place the generators. This should be apparent from your code.

My approach is such a situation is to "define your own generator" (assuming here that isSafe needs both its parameters):

pl `x` ql = [ (p,q) | p <-pl, q <- ql]

queens3 n =  map reverse $ queens' n

    where queens' 0       = [[]]                                                                                                

          queens' k       = [q:qs | (qs, q) <- queens' (k-1) `x` [1..n], isSafe q qs]                                              

          isSafe   try qs = not (try `elem` qs || sameDiag try qs)                                                              

          sameDiag try qs = any (\(colDist,q) -> abs (try - q) == colDist) $ zip [1..] qs

Of course you can make more refined versions of `x`, which perform all kinds of fair enumeration, but that is not the main point here. It is the fact that the parameters to `x` are only evaluated once which matters here.