Many times I have answered this. There is absolutely no difference between Siva and Vishnu! They are one and the same.

How many nostrils do you have? Two. What goes through them both? Air goes in and comes out from both the nostrils. Can you distinguish the air that comes out through the right nostril from that which comes from the left nostril? You cannot. But yet you refer to them distinctly as the right and left nostrils. Is there a difference between the two? No.

Similarly, there is no difference between Siva and Vishnu. They are one and the same.

(Q&A Bangalore 11 Nov 2015)