Pakistan will be the favorite going into the match but Pakistan is touring Bangladesh and on home soil they always have an advantage as they defeated other strong teams but after watching the World Cup they might not be a force in the shorter format but i am expecting them to perform well in the Test series. It wont be a one sided match and we can expect good competitive cricket in the Test format and the Test status is safe with Bangladesh when teams like Zimbabwe have Test status.
I don't think that Bangladesh will have any sort of home advantage. Against New Zealand, they were able to make use of the home advantage because the New Zealand bowlers struggled against spin on a track that resembled more like a dust bowl. But Pakistani batsmen are very talented in handling spin bowlers and they themselves have some of the best spinners in the world right now. So in case Bangladesh prepare dust bowls, then it will end up helping the Pakistanis. Bangladesh may be competitive, but Pakistan will be the favorites.