The 2 typical solutions are:
1. Copy the master list to the sync list.
2. Do an O(N*N) comparison between all element pairs.
You’ve excluded the smart options already: shared identity, sorting and change notifications.
Note that it’s not relevant whether the lists can be sorted in a meaningful way, or even completely. For instance, when comparing two string lists, it would be ideal to sort alphabetically. But the list comparison would still be more efficient if you’d sort both lists by string length! You’d still have to do a full pairwise comparison of strings of the same length, but that will probably be a much smaller nummber of pairs.