What are the basic differences in the attitudes of Lord Canterville and Mr. Otis?

The most basic attitude difference between Mr. Otis and Lord Canterville is their attitude toward the ghost.  
The attitude difference starts out as a difference in belief.  Lord Canterville believes that the ghost is real.  Mr. Otis does not believe the ghost of Sir Simon is real.  He even states that if ghosts were a real thing, then the Americans would already have one on display in a museum.  

"I have come from a modern country, where we have everything that money can buy; and with all our spry young fellows painting the Old World red, and carrying off your best actors and primadonnas, I reckon that if there were such a thing as a ghost in Europe, we'd have it at home in a very short time in one of our public museums, or on the road as a show."

Eventually, Mr. Otis comes to accept the fact that the ghost is real.  This leads to the second attitude difference between Lord Canterville and Mr. Otis.  Lord Canterville accepts the ghost's presence as an unfortunate consequence of the property.  He believes that nothing can be done about the ghost.  Mr. Otis, on the other hand, believes that the ghost problem can be solved.  Mr. Otis, and most of his family, view the ghost as a mild inconvenience of the home -- an inconvenience that can be fixed.  

"Upon the other hand," he continued, "if he really declines to use the Rising Sun Lubricator, we shall have to take his chains from him. It would be quite impossible to sleep, with such a noise going on outside the bedrooms."