I really wouldn't be too hard to hold French North America, with an addition 10,000 French professional soldiers. As things were the French were able to hold their own until the tide turned in 1758-1759. The British sent some fairly incompetent officers to the war front early on, and this of course helped the French. In addition, British settlers encroaching on Indian lands, won the French allies in the Ohio River Valley. The battle at Fort Carillon in July 1758 was a major French victory where French and Indian forces defeated a British-American force despite being outnumbered 5 to 1. Had Prussia been on France's side, enough French troops could have been diverted to New France to keep the British at bay and capture an important frontier settlement like Albany (which was seriously threatened in OTL).
In September 1757, Admiral Holbourne's fleet was badly damaged by a hurricane outside of Louisbourg harbour while the French ships were unscathed in the safety of the harbour. Had the French chased Holbourne's fleet he could have destroyed or captured 20 ships of the line with reinforcements effectively prevented troop reinforcements from arriving in America and given the French a chance to captured Albany and threaten New York.
Also, a Franco-Prussian alliance would have dramatically improved France's chances of victory in Europe as both countries had the largest and most effective armies on the continent. A continued Franco-Prussian alliance would have freed France from committing such a large number of troops to Europe.
The Austrian Netherlands can be overrun quickly, as the United Provinces contemporary sources seem to say that the government preferred to avoid war so that it could trade with both sides. In OTL the British requested Dutch assistance in the form of 6,000 troops on the continent, as per the Anglo-Dutch treaty, but this was refused. Also, the British began to intercept Dutch ships carrying naval stores to France from the Baltic throughout the war, angering the Dutch merchants, so more than likely the Dutch sit this one out.
If the Dutch remain neutral, Hanover and Brunswick will probably be mopped up by the French forces just as in OTL, leaving the Austrians having to face Prussia all alone.
The wildcard is of course Russia. Initially they were going to send troops through the Holy Roman Empire to assist in the defence of the United Provinces. However, these troops were to be subsidised by the British. If they're still a British ally, the French will have to contend with them. If they ally themselves with the British and Austrians against the French, this may draw the Swedes into the war.
As for Denmark, they were being paid a subsidy by the French to remain neutral. They still have the largest Baltic Navy and could close the Baltic off at Elsinore.