Housefull4 starcast will be like this Akki, Ritesh, John, sanjay dutt &3 heroine
So no varun/hritik
Housefull4 will lead in overseas,singham3 will lead in SS & mass areas
In multiplexes both will be more or less on par.
So Mumbai circuit will play the crucial role here which is the biggest circuit in India will be in favour of singham3,singham brand is huge in Maharashtra ,Gujarat.
So overall i think singham3 has upper hand on opening day, because as we know Ajay+Rohit combo in a big franchise movie is as big as a Khan movie.
So let's see,i think clash will happen because Temper will release towards 2018 end,so rohit has enough time to make singham3 before diwali & if singham turns out to be a good movie then it will definitely beat Housefull in long run also.