What would the USA be like today, a super power that is hated by the whole world or a big harmless country that everyone likes , sort of like a really big Canada?
First off the whole world does not hate the USA. Only the kind of people who the USA entered the war to fight against, hate the USA. The fascists the communists and the extremists of all kinds.
They don't like the USA because it mostly thwarts their aims. Some people in America try to spread the perception the America is hated because they want to to return to the kind of isolationism that Lindbergh and others espoused. It won't work and Americans enjoy the concept of freedom too much to sit idly by and let the world go to hell, literally in the WW2 case. It's not in the interests of American big business either.
So don't buy the lie that the USA is hated by most of the world.
But to return to the original question. I think the question itself is flawed. America was dragged into the war. America was in the way of Japan's ambition in the Far East They had to eliminate America's fleet and they tried to on December 7th. Hitler also gave the USA no choice by declaring war on it. America had no more choice than France, Poland or Holland. Holland was neutral but with Germany as a neighbour that option was not possible. Only Geographical separation and size prevented the same fate from befalling the USA.
American was in the way of Japan and Hitler's interests. The only possible way America could have stayed out of the war for Japan to be satisfied with it's foray into China and for Germany to remain within it's borders or at least it's claimed greater German borders.
In that case the post war world would probably be red in Europe. I think Germany would have become unstuck against the USSR in the end. The USSR really didn't need US aid it would simply have taken longer.
Once that war had finished, Stalin would have turned his attentions to Japan. Now that would be an interesting war.