Where possible, both the French and British used boats to move their artillery, actually the entire force - the French attack at Oswego; the British attack at Fort Frontenac several years later by Colonel Bradstreet (an aggressive, but competent British Officer). Once at the siege location, soldiers literally dragged the guns around.
It is my understanding, the french canadian militia, not the french regulars, literally manhandled the artillery pieces for the siege of Fort William Henry from Fort Carillon on Lake Ticonderoga to the upper end of Lake George --- a portage distance of several miles around the falls between Lake George and Lake Ticonderoga. I would think oxen were used to help, but from my reading, much was done with brute human strength - a herculean effort. Besides the cannon, all the boats used by Montcalm would have to have been moved from Lake Ticonderoga to Lake George by the portage road. Following the portage around the falls and rapids, the guns where then moved by boat to Fort William Henry. Following the battle, the whole cumbersome process would have had to be repeated in reverse.
The french guns were mounted on planks lashed between the hulls of two boats, simlar to a catamaran. But it is interesting to note, that some accounts have the French firing at least some of their artillery pieces from the water during the initial approach on Fort William Henry (sounds unplausible). From my reading, I get the impression the guns were mounted on their gun carriages while being transported on Lake George.
Someone once posted a thread showing how guns barrels were literally "rolled up" hills using ropes and pulleys when the terrain was particulary rough. This is one of the reasons why Braddock was so pleased to have the seaman with him at BoM, very efficient at using block and tackle. The guns captured at the Battle of Monongahela were moved to Fort Duquense by "canoe", presumably even the 12-pounders.
For long distance travel on land, the preferred method was to move the cannon and gun carriages separately, and then re-assemble them at the siege location. Otherwise, the damage done to the gun carriage by the extra weight of the barrel on rough roads would damage and weaken the gun carriage so much, that the carriage was no longer functional as an artillery platform. But I can find no mention of this problem as it regards Braddock's march.
The french gun carriages, ammunition wagons and limbers would have been more bulky and weighed more during the FIW than later in the 18th century or Napolean's day. During the FIW, the french limber would have carried significantly more shot and powder --- essentially, serving the function of an ammunition wagon. The extra weight and bulk of the earlier designs were not necessarily stronger. I believe that wheels on the french limbers would have been a smaller diameter during the FIW than later in the 18th century and not been a match for the wheels on the guns themselves.
There is a photo on page 7 of Osprey's Men-at Arms - 96 (Wise and Hook) that depicts "the older type of ammunition bearing limber" (French).
