With little-to-no resistance, the 4 cannons should survive long enough to take the city down to 0 hp, even if the city targets the cannons only. At least 2 cannons will survive long enough to take the remaining hp down, and the muskets can help block anything that tries to attack the cannons in melee. Ultimately, any other ranged units you have can join in the attack, and in the end, a single lancer can take the city when it's down to 0 hp.
Really, though, this all depends on terrain. In open terrain, it's 1 turn to move the cannons in, and 1 turn to set-up and start firing. But on rough terrain, or with an enemy Great Wall in place, it may take 2 turns to move the cannons into range, and then a third turn to actually set-up and fire. Moreover, sometimes obstructing terrain makes it so that the only spot your cannons can fire from is from tiles adjacent to the city itself, which adds the danger of the AI suddenly finishing production of a melee unit and killing a cannon with it.
So, the equation is not just your force vs a 41-str city, but also what the terrain is like, as that may mean an extra turn of city bombard on a unit while just moving up, let alone if the enemy has even just one or two ranged units that will also get an extra turn to attack. Which would very possibly make a difference.