Which countries emerged in a stronger position from the Seven Years' War?
Great Britain probably emerged stronger after the Seven Years War (also called the French and Indian War in North America). This makes sense since the British won the war. After the war the British gained control of Florida from the Spanish and Canada from the French. So after the war, Britain controlled all of North America east of the Mississippi River. In the long run, though, there were some important negative consequences for the British. With the elimination of the French west of the Appalachian Mountains, American colonists felt that they now had the right to move into these lands. As these colonists moved into these new lands, they came into conflict with the Native Americans there. The British government, reluctant to spend the money to defend the colonists against the Native Americans, passed the Proclamation of 1763 which stated that the colonists could not settle west of the Appalachians. This created some animosity between the colonists and the British government. In addition, the British government passed some tax laws in the colonies to pay for the Seven Years War, taxes that the American colonists greatly resented. Finally, with the end of the French presence in the area west of the Mississippi, the American colonists no longer felt the need for the presence of British soldiers in the colonies, and a separate American identity began to emerge in the colonies. These resentments, along with a growing American identity, led to the Revolutionary War. And it was in the Revolutionary War that the British lost control of North America east of the Mississippi River, including the return of Florida to the Spanish. They did retain control of Canada.
The two countries that emerged from this war in a stronger position (the ones that "won" the war) are Great Britain and Prussia. Prussia was a country that existed back in those days in Northern Europe -- in places that are now parts of Germany, Poland, etc.
Great Britain emerged as a winner in this war because France lost a lot of colonial territories. This was especially true in the Americas and in India. Britain took these territories (like Canada) away from the French and therefore emerged stronger. Prussia emerged as one of the biggest European powers because of the defeat of its biggest rival -- Austria.